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Hares and jackrabbits are mammals belonging to the genus Lepus. They are herbivores, and live solitarily or in pairs. They nest in slight depressions called forms, and their young are able to fend for themselves shortly after birth. The genus includes the largest lagomorphs. Most are fast runners with long, powerful hind legs, and large ears that dissipate body heat. Hare species are native to Africa, Eurasia and North America. A hare less than one year old is called a "leveret". A group of hares is called a "husk", a "down", or a "drove".
Members of the Lepus genus are considered true hares, distinguishing them from rabbits which make up the rest of the Leporidae family. However, there are five leporid species with "hare" in their common names which are not considered true hares: the hispid hare (Caprolagus hispidus), and four species known as red rock hares (Pronolagus). Conversely, several Lepus species are called "jackrabbits", but classed as hares rather than rabbits. The pet known as the Belgian hare is a domesticated European rabbit which has been selectively bred to resemble a hare.
Biology
Hares are swift animals and can run up to over short distances. Over longer distances, the European hare (Lepus europaeus) can run up to . The five species of jackrabbits found in central and western North America are able to run at over longer distances, and can leap up to at a time.
Normally a shy animal, the European brown hare changes its behavior in spring, when it can be seen in daytime chasing other hares. This appears to be competition between males (called bucks) to attain dominance for breeding. During this spring frenzy, animals of both sexes can be seen "boxing", one hare striking another with its paws. This behavior gives rise to the idiom "mad as a March hare". This is present not only in intermale competition, but also among females (called does) toward males to prevent copulation.
Differences from rabbits | Hare | Wikipedia | 448 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
Hares are generally larger than rabbits, with longer ears, and have black markings on their fur. Hares, like all leporids, have jointed, or kinetic, skulls, unique among mammals. They have 48 chromosomes, while rabbits have 44. Hares have not been domesticated, while some rabbits are raised for food and kept as pets.
Some rabbits live and give birth underground in burrows, with many burrows in an area forming a warren. Other rabbits and hares live and give birth in simple forms (shallow depression or flattened nest of grass) above the ground. Hares usually do not live in groups. Young hares are adapted to the lack of physical protection, relative to that afforded by a burrow, by being born fully furred and with eyes open. They are hence precocial, able to fend for themselves soon after birth. By contrast, rabbits are altricial, being born blind and hairless.
Diet
Easily digestible food is processed in the gastrointestinal tract, expelling the waste as regular feces. For nutrients that are harder to extract, hares, like all lagomorphs, ferment fiber in the cecum and expel the mass as cecotropes, which they ingest again, a practice called cecotrophy or refection. The cecotropes are absorbed in the small intestine to use the nutrients.
Classification
The 34 species listed are: | Hare | Wikipedia | 296 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
Genus Lepus
Subgenus Macrotolagus
Antelope jackrabbit, Lepus alleni
Subgenus Poecilolagus
Snowshoe hare, Lepus americanus
Subgenus Lepus
Arctic hare, Lepus arcticus
Alaskan hare, Lepus othus
Mountain hare, Lepus timidus
Subgenus Proeulagus
Black jackrabbit, Lepus insularis
Desert hare, Lepus tibetanus
Tolai hare, Lepus tolai
Subgenus Eulagos
Broom hare, Lepus castroviejoi
Yunnan hare, Lepus comus
Korean hare, Lepus coreanus
European hare, Lepus europaeus
Manchurian hare, Lepus mandshuricus
Ethiopian highland hare, Lepus starcki
Subgenus Sabanalagus
Ethiopian hare, Lepus fagani
African savanna hare, Lepus victoriae
Subgenus Indolagus
Hainan hare, Lepus hainanus
Indian hare, Lepus nigricollis
Burmese hare, Lepus peguensis
Subgenus Sinolagus
Chinese hare, Lepus sinensis
Subgenus Tarimolagus
Yarkand hare, Lepus yarkandensis
Incertae sedis
Tamaulipas jackrabbit, Lepus altamirae
Japanese hare, Lepus brachyurus
Black-tailed jackrabbit, Lepus californicus
White-sided jackrabbit, Lepus callotis
Cape hare, Lepus capensis
Corsican hare, Lepus corsicanus
Tehuantepec jackrabbit, Lepus flavigularis
Granada hare, Lepus granatensis
Abyssinian hare, Lepus habessinicus
Woolly hare, Lepus oiostolus
West Sahara hare, Lepus saharae
Scrub hare, Lepus saxatilis
White-tailed jackrabbit, Lepus townsendii
In human culture
Food
Meat
Hares and rabbits are plentiful in many areas, adapt to a wide variety of conditions, and reproduce quickly, so hunting is often less regulated than for other varieties of game. They are a common source of protein worldwide. Because of their extremely low fat content, they are a poor choice as a survival food.
Hares can be prepared in the same manner as rabbits—commonly roasted or parted for breading and frying.
(also spelled ) is a traditional German stew made from marinated rabbit or hare, seasoned with black pepper (German ) and other spices. Wine or vinegar is also a prominent ingredient, to lend a sourness to the recipe. | Hare | Wikipedia | 501 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
()—hare stew with pearl onions, vinegar, red wine, and cinnamon—is a much-prized dish enjoyed in Greece and Cyprus and communities in the diaspora.
The hare (and in recent times, the rabbit) is a staple of Maltese cuisine. The dish was presented to the island's Grandmasters of the Sovereign Military Order of Malta, as well as Renaissance Inquisitors resident on the island, several of whom went on to become pope.
According to Jewish tradition, the hare is among mammals deemed not kosher, and therefore not eaten by observant Jews. Muslims deem coney meat (rabbit, pika, hyrax) to be halal, and in Egypt, hare and rabbit are popular meats for mulukhiyah (jute leaf soup), especially in Cairo.
Blood
The blood of a freshly killed hare can be collected for consumption in a stew or casserole in a cooking process known as jugging. First the entrails are removed from the hare carcass before it is hung in a larder by its hind legs, which causes blood to accumulate in the chest cavity. One method of preserving the blood after draining it from the hare (since the hare is usually hung for a week or more) is to mix it with red wine vinegar to prevent coagulation, and then to store it in a freezer.
Jugged hare, known as in France, is a whole hare, cut into pieces, marinated, and cooked with red wine and juniper berries in a tall jug that stands in a pan of water. It traditionally is served with the hare's blood (or the blood is added right at the end of the cooking process) and port wine.
Jugged hare is described in an influential 18th-century English cookbook, The Art of Cookery by Hannah Glasse, with a recipe titled, "A Jugged Hare", that begins, "Cut it into little pieces, lard them here and there ..." The recipe goes on to describe cooking the pieces of hare in water in a jug set within a bath of boiling water to cook for three hours. In the 19th century, a myth arose that Glasse's recipe began with the words "First, catch your hare." | Hare | Wikipedia | 463 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
Many other British cookbooks from before the middle of the 20th century have recipes for jugged hare. Merle and Reitch have this to say about jugged hare, for example:
The best part of the hare, when roasted, is the loin and the thick part of the hind leg; the other parts are only fit for stewing, hashing, or jugging. It is usual to roast a hare first, and to stew or jug the portion which is not eaten the first day. ...
To Jug A Hare. This mode of cooking a hare is very desirable when there is any doubt as to its age, as an old hare, which would be otherwise uneatable, may be made into an agreeable dish.
In 2006, a survey of 2021 people for the UKTV Food television channel found only 1.6% of the people under 25 recognized jugged hare by name. Seven of ten stated they would refuse to eat jugged hare if it were served at the house of a friend or a relative.
In England, a now rarely served dish is potted hare. The hare meat is cooked, then covered in at least one inch (preferably more) of butter. The butter is a preservative (excludes air); the dish can be stored for up to several months. It is served cold, often on bread or as an appetizer.
Taming
No extant domesticated hares exist. However, hare remains have been found in a wide range of human settlement sites, some showing signs of use beyond simple hunting and eating:
A European brown hare was buried alongside an older woman in Hungary mid fifth millennium BC.
12 Mountain hare metapodials were found in a Swedish grave from third millennium BC.
The Tolai hare (originally described as a Cape hare, amended according to range) was tamed by northern Chinese people in the neolithic period (~third millennium BC) and fed millets.
In mythology and folklore
The hare in African folk tales is a trickster; some of the stories about the hare were retold among enslaved Africans in America and are the basis of the Br'er Rabbit stories. The hare appears in English folklore in the saying "as mad as a March hare" and in the legend of the White Hare that alternatively tells of a witch who takes the form of a white hare and goes out looking for prey at night or of the spirit of a broken-hearted maiden who cannot rest and who haunts her unfaithful lover. | Hare | Wikipedia | 506 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
The constellation Lepus is taken to represent a hare.
The hare was once regarded as an animal sacred to Aphrodite and Eros because of its high libido. Live hares were often presented as a gift of love. In European witchcraft, hares were either witches' familiars or a witch who had transformed themself into a hare. Now pop mythology associates the hare with the Anglo-Saxon goddess Ēostre as an explanation for the Easter Bunny, but is wholly modern in origin and has no authentic basis.
In European tradition, the hare symbolises the two qualities of swiftness and timidity. The latter once gave the European hare the Linnaean name Lepus timidus that is now limited to the mountain hare. Several ancient fables depict the Hare in flight: In one, The Hares and the Frogs, they decide to commit mass suicide to relieve the angst of constantly fleeing threats, but reconsider when they startle frogs on the way to throwing themselves into the river. Conversely, in The Tortoise and the Hare, perhaps the best-known among Aesop's Fables, the hare loses a race through being too confident in its swiftness. In Irish folklore, the hare is often associated with the Aos sí or other pagan elements. In these stories, characters who harm hares often suffer dreadful consequences.
In literature and art
In fiction
In art
Three hares
A study in 2004 followed the history and migration of a symbolic image of three hares with conjoined ears. In this image, three hares are seen chasing each other in a circle with their heads near its centre. While each of the animals appears to have two ears, only three ears are depicted. The ears form a triangle at the centre of the circle and each is shared by two of the hares. The image has been traced from Christian churches in the English county of Devon right back along the Silk Road to China, via western and eastern Europe and the Middle East. Before its appearance in China, it was possibly first depicted in the Middle East before being reimported centuries later. Its use is associated with Christian, Jewish, Islamic and Buddhist sites stretching back to about 600 CE.
Place names
The hare has given rise to local place names, as they can often be observed in favoured localities. An example in Scotland is "Murchland", "murchen" being a Scots word for a hare. | Hare | Wikipedia | 496 | 48130 | https://en.wikipedia.org/wiki/Hare | Biology and health sciences | Lagomorphs | null |
A microcomputer is a small, relatively inexpensive computer having a central processing unit (CPU) made out of a microprocessor. The computer also includes memory and input/output (I/O) circuitry together mounted on a printed circuit board (PCB). Microcomputers became popular in the 1970s and 1980s with the advent of increasingly powerful microprocessors. The predecessors to these computers, mainframes and minicomputers, were comparatively much larger and more expensive (though indeed present-day mainframes such as the IBM System z machines use one or more custom microprocessors as their CPUs). Many microcomputers (when equipped with a keyboard and screen for input and output) are also personal computers (in the generic sense). An early use of the term "personal computer" in 1962 predates microprocessor-based designs. (See "Personal Computer: Computers at Companies" reference below). A "microcomputer" used as an embedded control system may have no human-readable input and output devices. "Personal computer" may be used generically or may denote an IBM PC compatible machine.
The abbreviation "micro" was common during the 1970s and 1980s, but has since fallen out of common usage.
Origins
The term microcomputer came into popular use after the introduction of the minicomputer, although Isaac Asimov used the term in his short story "The Dying Night" as early as 1956 (published in The Magazine of Fantasy and Science Fiction in July that year). Most notably, the microcomputer replaced the many separate components that made up the minicomputer's CPU with one integrated microprocessor chip.
In 1973, the French Institut National de la Recherche Agronomique (INRA) was looking for a computer able to measure agricultural hygrometry. To answer this request, a team of French engineers of the computer technology company R2E, led by its Head of Development, François Gernelle, created the first available microprocessor-based microcomputer, the Micral N. The same year the company filed their patents with the term "Micro-ordinateur", a literal equivalent of "Microcomputer", to designate a solid state machine designed with a microprocessor. | Microcomputer | Wikipedia | 485 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
In the US the earliest models such as the Altair 8800 were often sold as kits to be assembled by the user, and came with as little as 256 bytes of RAM, and no input/output devices other than indicator lights and switches, useful as a proof of concept to demonstrate what such a simple device could do.
As microprocessors and semiconductor memory became less expensive, microcomputers grew cheaper and easier to use.
Increasingly inexpensive logic chips such as the 7400 series allowed cheap dedicated circuitry for improved user interfaces such as keyboard input, instead of simply a row of switches to toggle bits one at a time.
Use of audio cassettes for inexpensive data storage replaced manual re-entry of a program every time the device was powered on.
Large cheap arrays of silicon logic gates in the form of read-only memory and EPROMs allowed utility programs and self-booting kernels to be stored within microcomputers. These stored programs could automatically load further more complex software from external storage devices without user intervention, to form an inexpensive turnkey system that does not require a computer expert to understand or to use the device.
Random-access memory became cheap enough to afford dedicating approximately 1–2 kilobytes of memory to a video display controller frame buffer, for a 40x25 or 80x25 text display or blocky color graphics on a common household television. This replaced the slow, complex, and expensive teletypewriter that was previously common as an interface to minicomputers and mainframes.
All these improvements in cost and usability resulted in an explosion in their popularity during the late 1970s and early 1980s.
A large number of computer makers packaged microcomputers for use in small business applications. By 1979, many companies such as Cromemco, Processor Technology, IMSAI, North Star Computers, Southwest Technical Products Corporation, Ohio Scientific, Altos Computer Systems, Morrow Designs and others produced systems designed for resourceful end users or consulting firms to deliver business systems such as accounting, database management and word processing to small businesses. This allowed businesses unable to afford leasing of a minicomputer or time-sharing service the opportunity to automate business functions, without (usually) hiring a full-time staff to operate the computers. A representative system of this era would have used an S100 bus, an 8-bit processor such as an Intel 8080 or Zilog Z80, and either CP/M or MP/M operating system. | Microcomputer | Wikipedia | 507 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
The increasing availability and power of desktop computers for personal use attracted the attention of more software developers. As the industry matured, the market for personal computers standardized around IBM PC compatibles running DOS, and later Windows. Modern desktop computers, video game consoles, laptops, tablet PCs, and many types of handheld devices, including mobile phones, pocket calculators, and industrial embedded systems, may all be considered examples of microcomputers according to the definition given above. | Microcomputer | Wikipedia | 95 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
Colloquial use of the term
By the early 2000s, everyday use of the expression "microcomputer" (and in particular "micro") declined significantly from its peak in the mid-1980s. The term is most commonly associated with the most popular 8-bit home computers (such as the Apple II, ZX Spectrum, Commodore 64, BBC Micro, and TRS-80) and small-business CP/M-based microcomputers.
In colloquial usage, "microcomputer" has been largely supplanted by the term "personal computer" or "PC", which specifies a computer that has been designed to be used by one individual at a time, a term first coined in 1959. IBM first promoted the term "personal computer" to differentiate the IBM PC from CP/M-based microcomputers likewise targeted at the small-business market, and also IBM's own mainframes and minicomputers. However, following its release, the IBM PC itself was widely imitated, as well as the term. The component parts were commonly available to producers and the BIOS was reverse engineered through cleanroom design techniques. IBM PC compatible "clones" became commonplace, and the terms "personal computer", and especially "PC", stuck with the general public, often specifically for a computer compatible with DOS (or nowadays Windows).
Description
Monitors, keyboards and other devices for input and output may be integrated or separate. Computer memory in the form of RAM, and at least one other less volatile, memory storage device are usually combined with the CPU on a system bus in one unit. Other devices that make up a complete microcomputer system include batteries, a power supply unit, a keyboard and various input/output devices used to convey information to and from a human operator (printers, monitors, human interface devices). Microcomputers are designed to serve only one user at a time, although they can often be modified with software or hardware to concurrently serve more than one user. Microcomputers fit well on or under desks or tables, so that they are within easy access of users. Bigger computers like minicomputers, mainframes, and supercomputers take up large cabinets or even dedicated rooms. | Microcomputer | Wikipedia | 466 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
A microcomputer comes equipped with at least one type of data storage, usually RAM. Although some microcomputers (particularly early 8-bit home micros) perform tasks using RAM alone, some form of secondary storage is normally desirable. In the early days of home micros, this was often a data cassette deck (in many cases as an external unit). Later, secondary storage (particularly in the form of floppy disk and hard disk drives) were built into the microcomputer case.
History
TTL precursors
Although they did not contain any microprocessors, but were built around transistor-transistor logic (TTL), Hewlett-Packard calculators as far back as 1968 had various levels of programmability comparable to microcomputers. The HP 9100B (1968) had rudimentary conditional (if) statements, statement line numbers, jump statements (go to), registers that could be used as variables, and primitive subroutines. The programming language resembled assembly language in many ways. Later models incrementally added more features, including the BASIC programming language (HP 9830A in 1971). Some models had tape storage and small printers. However, displays were limited to one line at a time. The HP 9100A was referred to as a personal computer in an advertisement in a 1968 Science magazine, but that advertisement was quickly dropped. HP was reluctant to sell them as "computers" because the perception at that time was that a computer had to be big in size to be powerful, and thus decided to market them as calculators. Additionally, at that time, people were more likely to buy calculators than computers, and, purchasing agents also preferred the term "calculator" because purchasing a "computer" required additional layers of purchasing authority approvals.
The Datapoint 2200, made by CTC in 1970, was also comparable to microcomputers. While it contains no microprocessor, the instruction set of its custom TTL processor was the basis of the instruction set for the Intel 8008, and for practical purposes the system behaves approximately as if it contains an 8008. This is because Intel was the contractor in charge of developing the Datapoint's CPU, but ultimately CTC rejected the 8008 design because it needed 20 support chips. | Microcomputer | Wikipedia | 482 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
Another early system, the Kenbak-1, was released in 1971. Like the Datapoint 2200, it used small-scale integrated transistor–transistor logic instead of a microprocessor. It was marketed as an educational and hobbyist tool, but it was not a commercial success; production ceased shortly after introduction.
Early microcomputers
In late 1972, a French team headed by François Gernelle within a small company, Réalisations & Etudes Electroniques (R2E), developed and patented a computer based on a microprocessor – the Intel 8008 8-bit microprocessor. This Micral-N was marketed in early 1973 as a "Micro-ordinateur" or microcomputer, mainly for scientific and process-control applications. About a hundred Micral-N were installed in the next two years, followed by a new version based on the Intel 8080. Meanwhile, another French team developed the Alvan, a small computer for office automation which found clients in banks and other sectors. The first version was based on LSI chips with an Intel 8008 as peripheral controller (keyboard, monitor and printer), before adopting the Zilog Z80 as main processor.
In late 1972, a Sacramento State University team led by Bill Pentz built the Sac State 8008 computer, able to handle thousands of patients' medical records. The Sac State 8008 was designed with the Intel 8008. It had a full set of hardware and software components: a disk operating system included in a series of programmable read-only memory chips (PROMs); 8 Kilobytes of RAM; IBM's Basic Assembly Language (BAL); a hard drive; a color display; a printer output; a 150 bit/s serial interface for connecting to a mainframe; and even the world's first microcomputer front panel.
In early 1973, Sord Computer Corporation (now Toshiba Personal Computer System Corporation) completed the SMP80/08, which used the Intel 8008 microprocessor. The SMP80/08, however, did not have a commercial release. After the first general-purpose microprocessor, the Intel 8080, was announced in April 1974, Sord announced the SMP80/x, the first microcomputer to use the 8080, in May 1974. | Microcomputer | Wikipedia | 491 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
Virtually all early microcomputers were essentially boxes with lights and switches; one had to read and understand binary numbers and machine language to program and use them (the Datapoint 2200 was a striking exception, bearing a modern design based on a monitor, keyboard, and tape and disk drives). Of the early "box of switches"-type microcomputers, the MITS Altair 8800 (1975) was arguably the most famous. Most of these simple, early microcomputers were sold as electronic kits—bags full of loose components which the buyer had to solder together before the system could be used.
The period from about 1971 to 1976 is sometimes called the first generation of microcomputers. Many companies such as DEC, National Semiconductor, Texas Instruments offered their microcomputers for use in terminal control, peripheral device interface control and industrial machine control. There were also machines for engineering development and hobbyist personal use. In 1975, the Processor Technology SOL-20 was designed, which consisted of one board which included all the parts of the computer system. The SOL-20 had built-in EPROM software which eliminated the need for rows of switches and lights. The MITS Altair just mentioned played an instrumental role in sparking significant hobbyist interest, which itself eventually led to the founding and success of many well-known personal computer hardware and software companies, such as Microsoft and Apple Computer. Although the Altair itself was only a mild commercial success, it helped spark a huge industry.
Home computers
By 1977, the introduction of the second microcomputer generation as consumer goods, known as home computers, made them considerably easier to use than their predecessors because their predecessors' operation often demanded thorough familiarity with practical electronics. The ability to connect to a monitor (screen) or TV set allowed visual manipulation of text and numbers. The BASIC language, which was easier to learn and use than raw machine language, became a standard feature. These features were already common in minicomputers, with which many hobbyists and early produces were familiar.
In 1979, the launch of the VisiCalc spreadsheet (initially for the Apple II) first turned the microcomputer from a hobby for computer enthusiasts into a business tool. After the 1981 release by IBM of its IBM PC, the term personal computer became generally used for microcomputers compatible with the IBM PC architecture (IBM PC–compatible). | Microcomputer | Wikipedia | 490 | 48144 | https://en.wikipedia.org/wiki/Microcomputer | Technology | Computer hardware | null |
A fossil fuel is a carbon compound- or hydrocarbon-containing material formed naturally in the Earth's crust from the buried remains of prehistoric organisms (animals, plants or planktons), a process that occurs within geological formations. Reservoirs of such compound mixtures, such as coal, petroleum and natural gas, can be extracted and burnt as fuel for human consumption to provide energy for direct use (such as for cooking, heating or lighting), to power heat engines (such as steam or internal combustion engines) that can propel vehicles, or to generate electricity via steam turbine generators. Some fossil fuels are further refined into derivatives such as kerosene, gasoline and diesel, or converted into petrochemicals such as polyolefins (plastics), aromatics and synthetic resins.
The origin of fossil fuels is the anaerobic decomposition of buried dead organisms. The conversion from these organic materials to high-carbon fossil fuels typically requires a geological process of millions of years. Due to the length of time it takes nature to form them, fossil fuels are considered non-renewable resources.
In 2022, over 80% of primary energy consumption in the world and over 60% of its electricity supply were from fossil fuels. The large-scale burning of fossil fuels causes serious environmental damage. Over 70% of the greenhouse gas emissions due to human activity in 2022 was carbon dioxide () released from burning fossil fuels. Natural carbon cycle processes on Earth, mostly absorption by the ocean, can remove only a small part of this, and terrestrial vegetation loss due to deforestation, land degradation and desertification further compounds this deficiency. Therefore, there is a net increase of many billion tonnes of atmospheric per year. Although methane leaks are significant, the burning of fossil fuels is the main source of greenhouse gas emissions causing global warming and ocean acidification. Additionally, most air pollution deaths are due to fossil fuel particulates and noxious gases, and it is estimated that this costs over 3% of the global gross domestic product and that fossil fuel phase-out will save millions of lives each year. | Fossil fuel | Wikipedia | 420 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
Recognition of the climate crisis, pollution and other negative impacts caused by fossil fuels has led to a widespread policy transition and activist movement focused on ending their use in favor of renewable and sustainable energy. Because the fossil-fuel industry is so heavily integrated in the global economy and heavily subsidized, this transition is expected to have significant economic impacts. Many stakeholders argue that this change needs to be a just transition and create policy that addresses the societal burdens created by the stranded assets of the fossil fuel industry. International policy, in the form of United Nations' sustainable development goals for affordable and clean energy and climate action, as well as the Paris Climate Agreement, is designed to facilitate this transition at a global level. In 2021, the International Energy Agency concluded that no new fossil fuel extraction projects could be opened if the global economy and society wants to avoid the worst impacts of climate change and meet international goals for climate change mitigation.
Origin
The theory that fossil fuels formed from the fossilized remains of dead plants by exposure to heat and pressure in Earth's crust over millions of years was first introduced by Andreas Libavius "in his 1597 Alchemia [Alchymia]" and later by Mikhail Lomonosov "as early as 1757 and certainly by 1763". The first recorded use of the term "fossil fuel" occurs in the work of the German chemist Caspar Neumann, in English translation in 1759. The Oxford English Dictionary notes that in the phrase "fossil fuel" the adjective "fossil" means "[o]btained by digging; found buried in the earth", which dates to at least 1652, before the English noun "fossil" came to refer primarily to long-dead organisms in the early 18th century.
Aquatic phytoplankton and zooplankton that died and sedimented in large quantities under anoxic conditions millions of years ago began forming petroleum and natural gas as a result of anaerobic decomposition. Over geological time this organic matter, mixed with mud, became buried under further heavy layers of inorganic sediment. The resulting high temperature and pressure caused the organic matter to chemically alter, first into a waxy material known as kerogen, which is found in oil shales, and then with more heat into liquid and gaseous hydrocarbons in a process known as catagenesis. Despite these heat-driven transformations, the energy released in combustion is still photosynthetic in origin. | Fossil fuel | Wikipedia | 495 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
Terrestrial plants tended to form coal and methane. Many of the coal fields date to the Carboniferous period of Earth's history. Terrestrial plants also form type III kerogen, a source of natural gas. Although fossil fuels are continually formed by natural processes, they are classified as non-renewable resources because they take millions of years to form and known viable reserves are being depleted much faster than new ones are generated.
Importance
Fossil fuels have been important to human development because they can be readily burned in the open atmosphere to produce heat. The use of peat as a domestic fuel predates recorded history. Coal was burned in some early furnaces for the smelting of metal ore, while semi-solid hydrocarbons from oil seeps were also burned in ancient times, they were mostly used for waterproofing and embalming.
Commercial exploitation of petroleum began in the 19th century.
Natural gas, once flared-off as an unneeded byproduct of petroleum production, is now considered a very valuable resource. Natural gas deposits are also the main source of helium.
Heavy crude oil, which is much more viscous than conventional crude oil, and oil sands, where bitumen is found mixed with sand and clay, began to become more important as sources of fossil fuel in the early 2000s. Oil shale and similar materials are sedimentary rocks containing kerogen, a complex mixture of high-molecular weight organic compounds, which yield synthetic crude oil when heated (pyrolyzed). With additional processing, they can be employed instead of other established fossil fuels. During the 2010s and 2020s there was disinvestment from exploitation of such resources due to their high carbon cost relative to more easily-processed reserves. | Fossil fuel | Wikipedia | 344 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
Prior to the latter half of the 18th century, windmills and watermills provided the energy needed for work such as milling flour, sawing wood or pumping water, while burning wood or peat provided domestic heat. The wide-scale use of fossil fuels, coal at first and petroleum later, in steam engines enabled the Industrial Revolution. At the same time, gas lights using natural gas or coal gas were coming into wide use. The invention of the internal combustion engine and its use in automobiles and trucks greatly increased the demand for gasoline and diesel oil, both made from fossil fuels. Other forms of transportation, railways and aircraft, also require fossil fuels. The other major use for fossil fuels is in generating electricity and as feedstock for the petrochemical industry. Tar, a leftover of petroleum extraction, is used in the construction of roads.
The energy for the Green Revolution was provided by fossil fuels in the form of fertilizers (natural gas), pesticides (oil), and hydrocarbon-fueled irrigation. The development of synthetic nitrogen fertilizer has significantly supported global population growth; it has been estimated that almost half of the Earth's population are currently fed as a result of synthetic nitrogen fertilizer use. According to head of a fertilizers commodity price agency, "50% of the world's food relies on fertilisers."
Environmental effects
The burning of fossil fuels has a number of negative externalitiesharmful environmental impacts where the effects extend beyond the people using the fuel. These effects vary between different fuels. All fossil fuels release when they burn, thus accelerating climate change. Burning coal, and to a lesser extent oil and its derivatives, contributes to atmospheric particulate matter, smog and acid rain.
Air pollution from fossil fuels in 2018 has been estimated to cost US$2.9 trillion, or 3.3% of the global gross domestic product (GDP).
Climate change is largely driven by the release of greenhouse gases like , and the burning of fossil fuels is the main source of these emissions. In most parts of the world climate change is negatively impacting ecosystems. This includes contributing to the extinction of species and reducing people's ability to produce food, thus adding to the problem of world hunger. Continued rises in global temperatures will lead to further adverse effects on both ecosystems and people; the World Health Organization has said that climate change is the greatest threat to human health in the 21st century. | Fossil fuel | Wikipedia | 494 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
Combustion of fossil fuels generates sulfuric and nitric acids, which fall to Earth as acid rain, impacting both natural areas and the built environment. Monuments and sculptures made from marble and limestone are particularly vulnerable, as the acids dissolve calcium carbonate.
Fossil fuels also contain radioactive materials, mainly uranium and thorium, which are released into the atmosphere. In 2000, about 12,000 tonnes of thorium and 5,000 tonnes of uranium were released worldwide from burning coal. It is estimated that during 1982, US coal burning released 155 times as much radioactivity into the atmosphere as the Three Mile Island accident.
Burning coal also generates large amounts of bottom ash and fly ash. These materials are used in a wide variety of applications (see Fly ash reuse), utilizing, for example, about 40% of the United States production.
In addition to the effects that result from burning, the harvesting, processing, and distribution of fossil fuels also have environmental effects. Coal mining methods, particularly mountaintop removal and strip mining, have negative environmental impacts, and offshore oil drilling poses a hazard to aquatic organisms. Fossil fuel wells can contribute to methane release via fugitive gas emissions. Oil refineries also have negative environmental impacts, including air and water pollution. Coal is sometimes transported by diesel-powered locomotives, while crude oil is typically transported by tanker ships, requiring the combustion of additional fossil fuels.
A variety of mitigating efforts have arisen to counter the negative effects of fossil fuels. This includes a movement to use alternative energy sources, such as renewable energy. Environmental regulation uses a variety of approaches to limit these emissions; for example, rules against releasing waste products like fly ash into the atmosphere.
In December 2020, the United Nations released a report saying that despite the need to reduce greenhouse emissions, various governments are "doubling down" on fossil fuels, in some cases diverting over 50% of their COVID-19 recovery stimulus funding to fossil fuel production rather than to alternative energy. The UN secretary general António Guterres declared that "Humanity is waging war on nature. This is suicidal. Nature always strikes backand it is already doing so with growing force and fury." He also claimed there is still cause for hope, anticipating the US plan to join other large emitters like China and the EU in adopting targets to reach net zero emissions by 2050.
Inflation effects
Fossilflation is a term that describes the impact of fossil fuels on inflation. | Fossil fuel | Wikipedia | 491 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
According to Vox in August 2022, "Economists have pointed to energy prices as the main reason for high inflation," noting that "energy prices indirectly affect virtually every part of the economy". Sectors that raise prices significantly as a result of higher fossil fuel prices include transportation, food, and shipping.
History
Mark Zandi of Moody's says that fossil fuel prices have driven every big episode of inflation since WWII.
The economic impact of the Russian Invasion of Ukraine in 2022 was a major recent example of fossil fuels causing inflation. Some economists, including Isabel Schnabel, believe that dependence on fossil fuels is the main driver of the 2021-2022 inflation spike.
Efforts to combat fossilflation
Gernot Wagner argues that commodities are undesirable energy sources because they are susceptible to volatile price swings that technologies like renewable energy are not. He also argues that technologies improve and get relatively cheaper over time. Coming out of the COVID-19 pandemic, some argued for the possibility of a base effect phenomenon due to cheaper than normal prices, such as for oil, at the onset of the pandemic, followed by above-average prices which exacerbated the perceived inflation.
Inflation Reduction Act
While not expected to provide much short-term relief, the Inflation Reduction Act seeks to make the United States less dependent on fossil fuels and their ability to cause inflation in the economy. Moody's estimates that by 2030, the bill could reduce the typical American household's spending on energy by more than $300 each year, in 2022 dollars.
Illness and deaths
Environmental pollution from fossil fuels impacts humans because particulates and other air pollution from fossil fuel combustion may cause illness and death when inhaled. These health effects include premature death, acute respiratory illness, aggravated asthma, chronic bronchitis and decreased lung function. The poor, undernourished, very young and very old, and people with preexisting respiratory disease and other ill health are more at risk. Global air pollution deaths due to fossil fuels have been estimated at over 8 million people (2018, nearly 1 in 5 deaths worldwide) at 10.2 million (2019), and 5.13 million excess deaths from ambient air pollution from fossil fuel use (2023). | Fossil fuel | Wikipedia | 456 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
While all energy sources inherently have adverse effects, the data show that fossil fuels cause the highest levels of greenhouse gas emissions and are the most dangerous for human health. In contrast, modern renewable energy sources appear to be safer for human health and cleaner. The death rates from accidents and air pollution in the EU are as follows per terawatt-hour (TWh):
As the data shows, coal, oil, natural gas, and biomass cause higher death rates and higher levels of greenhouse gas emissions than hydropower, nuclear energy, wind, and solar power. Scientists propose that 1.8 million lives have been saved by replacing fossil fuel sources with nuclear power.
Phase-out
Just transition
Divestment
Industrial sector
In 2019, Saudi Aramco was listed and it reached a US$2 trillion valuation on its second day of trading, after the world's largest initial public offering.
Subsidies
Lobbying activities | Fossil fuel | Wikipedia | 181 | 48146 | https://en.wikipedia.org/wiki/Fossil%20fuel | Technology | Energy | null |
In astronomy and navigation, the celestial sphere is an abstract sphere that has an arbitrarily large radius and is concentric to Earth. All objects in the sky can be conceived as being projected upon the inner surface of the celestial sphere, which may be centered on Earth or the observer. If centered on the observer, half of the sphere would resemble a hemispherical screen over the observing location.
The celestial sphere is a conceptual tool used in spherical astronomy to specify the position of an object in the sky without consideration of its linear distance from the observer. The celestial equator divides the celestial sphere into northern and southern hemispheres.
Description
Because astronomical objects are at such remote distances, casual observation of the sky offers no information on their actual distances. All celestial objects seem equally far away, as if fixed onto the inside of a sphere with a large but unknown radius, which appears to rotate westward overhead; meanwhile, Earth underfoot seems to remain still. For purposes of spherical astronomy, which is concerned only with the directions to celestial objects, it makes no difference if this is actually the case or if it is Earth that is rotating while the celestial sphere is stationary.
The celestial sphere can be considered to be infinite in radius. This means any point within it, including that occupied by the observer, can be considered the center. It also means that all parallel lines, be they millimetres apart or across the Solar System from each other, will seem to intersect the sphere at a single point, analogous to the vanishing point of graphical perspective. All parallel planes will seem to intersect the sphere in a coincident great circle (a "vanishing circle").
Conversely, observers looking toward the same point on an infinite-radius celestial sphere will be looking along parallel lines, and observers looking toward the same great circle, along parallel planes. On an infinite-radius celestial sphere, all observers see the same things in the same direction.
For some objects, this is over-simplified. Objects which are relatively near to the observer (for instance, the Moon) will seem to change position against the distant celestial sphere if the observer moves far enough, say, from one side of planet Earth to the other. This effect, known as parallax, can be represented as a small offset from a mean position. The celestial sphere can be considered to be centered at the Earth's center, the Sun's center, or any other convenient location, and offsets from positions referred to these centers can be calculated. | Celestial sphere | Wikipedia | 498 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
In this way, astronomers can predict geocentric or heliocentric positions of objects on the celestial sphere, without the need to calculate the individual geometry of any particular observer, and the utility of the celestial sphere is maintained. Individual observers can work out their own small offsets from the mean positions, if necessary. In many cases in astronomy, the offsets are insignificant.
Determining location of objects
The celestial sphere can thus be thought of as a kind of astronomical shorthand, and is applied very frequently by astronomers. For instance, the Astronomical Almanac for 2010 lists the apparent geocentric position of the Moon on January 1 at 00:00:00.00 Terrestrial Time, in equatorial coordinates, as right ascension 6h 57m 48.86s, declination +23° 30' 05.5". Implied in this position is that it is as projected onto the celestial sphere; any observer at any location looking in that direction would see the "geocentric Moon" in the same place against the stars. For many rough uses (e.g. calculating an approximate phase of the Moon), this position, as seen from the Earth's center, is adequate.
For applications requiring precision (e.g. calculating the shadow path of an eclipse), the Almanac gives formulae and methods for calculating the topocentric coordinates, that is, as seen from a particular place on the Earth's surface, based on the geocentric position. This greatly abbreviates the amount of detail necessary in such almanacs, as each observer can handle their own specific circumstances. | Celestial sphere | Wikipedia | 321 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
Greek history on celestial spheres
Celestial spheres (or celestial orbs) were envisioned to be perfect and divine entities initially from Greek astronomers such as Aristotle. He composed a set of principles called Aristotelian physics that outlined the natural order and structure of the world. Like other Greek astronomers, Aristotle also thought the "...celestial sphere as the frame of reference for their geometric theories of the motions of the heavenly bodies". With his adoption of Eudoxus of Cnidus' theory, Aristotle had described celestial bodies within the Celestial sphere to be filled with pureness, perfect and quintessence (the fifth element that was known to be divine and purity according to Aristotle). Aristotle deemed the Sun, Moon, planets and the fixed stars to be perfectly concentric spheres in a superlunary region above the sublunary sphere. Aristotle had asserted that these bodies (in the superlunary region) are perfect and cannot be corrupted by any of the classical elements: fire, water, air, and earth. Corruptible elements were only contained in the sublunary region and incorruptible elements were in the superlunary region of Aristotle's geocentric model. Aristotle had the notion that celestial orbs must exhibit celestial motion (a perfect circular motion) that goes on for eternity. He also argued that the behavior and property follows strictly to a principle of natural place where the quintessential element moves freely of divine will, while other elements, fire, air, water and earth, are corruptible, subject to change and imperfection. Aristotle's key concepts rely on the nature of the five elements distinguishing the Earth and the Heavens in the astronomical reality, taking Eudoxus's model of separate spheres. | Celestial sphere | Wikipedia | 352 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
Numerous discoveries from Aristotle and Eudoxus (approximately 395 B.C. to 337 B.C.) have sparked differences in both of their models and sharing similar properties simultaneously. Aristotle and Eudoxus claimed two different counts of spheres in the heavens. According to Eudoxus, there were only 27 spheres in the heavens, while there are 55 spheres in Aristotle's model. Eudoxus attempted to construct his model mathematically from a treatise known as On Speeds () and asserted the shape of the hippopede or lemniscate was associated with planetary retrogression. Aristotle emphasized that the speed of the celestial orbs is unchanging, like the heavens, while Eudoxus emphasized that the orbs are in a perfect geometrical shape. Eudoxus's spheres would produce undesirable motions to the lower region of the planets, while Aristotle introduced unrollers between each set of active spheres to counteract the motions of the outer set, or else the outer motions will be transferred to the outer planets. Aristotle would later observe "...the motions of the planets by using the combinations of nested spheres and circular motions in creative ways, but further observations kept undoing their work".
Aside from Aristotle and Eudoxus, Empedocles gave an explanation that the motion of the heavens, moving about it at divine (relatively high) speed, puts the Earth in a stationary position due to the circular motion preventing the downward movement from natural causes. Aristotle criticized Empedocles's model, arguing that all heavy objects go towards the Earth and not the whirl itself coming to Earth. He ridiculed it and claimed that Empedocles's statement was extremely absurd. Anything that defied the motion of natural place and the unchanging heavens (including the celestial spheres) was criticized immediately by Aristotle. | Celestial sphere | Wikipedia | 384 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
==Celestial coordinate systems==
These concepts are important for understanding celestial coordinate systems, frameworks for measuring the positions of objects in the sky. Certain reference lines and planes on Earth, when projected onto the celestial sphere, form the bases of the reference systems. These include the Earth's equator, axis, and orbit. At their intersections with the celestial sphere, these form the celestial equator, the north and south celestial poles, and the ecliptic, respectively. As the celestial sphere is considered arbitrary or infinite in radius, all observers see the celestial equator, celestial poles, and ecliptic at the same place against the background stars.
From these bases, directions toward objects in the sky can be quantified by constructing celestial coordinate systems. Similar to geographic longitude and latitude, the equatorial coordinate system specifies positions relative to the celestial equator and celestial poles, using right ascension and declination. The ecliptic coordinate system specifies positions relative to the ecliptic (Earth's orbit), using ecliptic longitude and latitude. Besides the equatorial and ecliptic systems, some other celestial coordinate systems, like the galactic coordinate system, are more appropriate for particular purposes.
History | Celestial sphere | Wikipedia | 238 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
The ancient Greeks assumed the literal truth of stars attached to a celestial sphere, revolving about the Earth in one day, and a fixed Earth.
The Eudoxan planetary model, on which the Aristotelian and Ptolemaic models were based, was the first geometric explanation for the "wandering" of the classical planets. The outermost of these "crystal spheres" was thought to carry the fixed stars. Eudoxus used 27 concentric spherical solids to answer Plato's challenge: "By the assumption of what uniform and orderly motions can the apparent motions of the planets be accounted for?"
Anaxagoras in the mid 5th century BC was the first known philosopher to suggest that the stars were "fiery stones" too far away for their heat to be felt. Similar ideas were expressed by Aristarchus of Samos. However, they did not enter mainstream European and Islamic astronomy of the late ancient and medieval period.
Copernican heliocentrism did away with the planetary spheres, but it did not necessarily preclude the existence of a sphere for the fixed stars. The first astronomer of the European Renaissance to suggest that the stars were distant suns was Giordano Bruno in his De l'infinito universo et mondi (1584). This idea was among the charges, albeit not in a prominent position, brought against him by the Inquisition.
The idea became mainstream in the later 17th century, especially following the publication of Conversations on the Plurality of Worlds by Bernard Le Bovier de Fontenelle (1686), and by the early 18th century it was the default working assumptions in stellar astronomy.
Star globe
A celestial sphere can also refer to a physical model of the celestial sphere or celestial globe.
Such globes map the constellations on the outside of a sphere, resulting in a mirror image of the constellations as seen from Earth. The oldest surviving example of such an artifact is the globe of the Farnese Atlas sculpture, a 2nd-century copy of an older (Hellenistic period, ca. 120 BCE) work.
Bodies other than Earth
Observers on other worlds would, of course, see objects in that sky under much the same conditions – as if projected onto a dome. Coordinate systems based on the sky of that world could be constructed. These could be based on the equivalent "ecliptic", poles and equator, although the reasons for building a system that way are as much historic as technical. | Celestial sphere | Wikipedia | 496 | 48239 | https://en.wikipedia.org/wiki/Celestial%20sphere | Physical sciences | Celestial sphere | null |
The lagomorphs () are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (rabbits and hares) and the Ochotonidae (pikas). There are 110 recent species of lagomorph, of which only 109 species in twelve genera are extant, including ten genera of rabbits (42 species); one genus of hare (33 species) and one genus of pika (34 species). The name of the order is derived from the Ancient Greek lagos (λαγώς, "hare") + morphē (μορφή, "form").
Taxonomy and evolutionary history
Other names used for this order, now considered synonymous, include: Duplicidentata (Illiger, 1811); Leporida (Averianov, 1999); Neolagomorpha (Averianov, 1999); Ochotonida (Averianov, 1999); and Palarodentia (Haeckel, 1895; Lilian, 2016).
The evolutionary history of the lagomorphs is still not well understood. In the late 20th century, it was generally agreed that Eurymylus, which lived in eastern Asia and dates back to the late Paleocene or early Eocene, was an ancestor of the lagomorphs. Examination of the fossil evidence in the 21st century suggested that the lagomorphs may have instead descended from mimotonids, mammals present in Asia during the Paleogene with similar body size and dental structure to early European rabbits such as Megalagus turgidus, while Eurymylus was more closely related to rodents (although not a direct ancestor). The leporids first appeared in the late Eocene and rapidly spread throughout the Northern Hemisphere; they show a trend towards increasingly long hind limbs as the modern leaping gait developed. The pikas appeared somewhat later in the Oligocene of eastern Asia.
Lagomorphs were certainly more diverse in the past than in the present, with around 75 genera and over 230 species represented in the fossil record and many more species in a single biome. This is evidence that lagomorph lineages are declining.
A 2008 study suggests an Indian origin for the order, having possibly evolved in isolation when India was an island continent in the Paleocene. | Lagomorpha | Wikipedia | 491 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Characteristics
Lagomorphs are similar to other mammals in that they all have hair, four limbs (i.e., they are tetrapods), and mammary glands and are endotherms. Lagomorphs possess a moderately fused postorbital process to the cranium, unlike other small mammals. They differ in that they have a mixture of "basal" and "derived" physical traits.
Differences between lagomorphs and other mammals
Lagomorphs and rodents form the clade or grandorder Glires. Despite the evolutionary relationship between lagomorphs and rodents, the two orders have some major differences.
Lagomorphs have four incisors in the upper jaw (smaller peg teeth behind larger incisors), whereas rodents only have two. They are similar to rodents in that their incisors grow continuously, thus necessitating constant chewing on fibrous food to prevent the teeth from growing too long. In addition, all lagomorph teeth grow continuously, while for most rodents, only the incisors grow continuously. Lagomorph and rodent incisors are structured differently. Lagomorphs have more cheek teeth than rodents. Both have a large diastema.
Lagomorphs are almost strictly herbivorous, unlike rodents, many of which will eat both meat and vegetable matter. Lagomorphs have no paw pads; instead, the bottoms of their paws are entirely covered with fur, a trait they share with red pandas. Similar to the rodents, bats, and some mammalian insectivores, they have a smooth-surfaced cerebrum. Lagomorphs are unusual among terrestrial mammals in that the females are larger than males.
Differences between families of lagomorphs
Rabbits and hares move by jumping, pushing off with their strong hind legs and using their forelimbs to soften the impact on landing. Pikas lack certain skeletal modifications present in leporids, such as a highly arched skull, an upright posture of the head, strong hind limbs and pelvic girdle, and long limbs. Also, pikas have a short nasal region and entirely lack a supraorbital foramen, while leporids have prominent supraorbital foramina and nasal regions.
Pikas | Lagomorpha | Wikipedia | 485 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Pikas, also known as conies, are entirely represented by the family Ochotonidae and are small mammals native to mountainous regions of western North America and Central Asia. They are mostly about long and have greyish-brown, silky fur, small rounded ears, and almost no tail. Their four legs are nearly equal in length. Some species live in scree, making their homes in the crevices between broken rocks, while others construct burrows in upland areas. The rock-dwelling species are typically long-lived and solitary, having one or two small litters each year contributing to stable populations. The burrowing species, in contrast, are short-lived, gregarious and have multiple large litters during the year. These species tend to have large swings in population size. The gestation period of the pika is around one month long, and the newborns are altricial (eyes and ears closed, no fur). The social behaviour of the two groups also differs: the rock dwellers aggressively maintain scent-marked territories, while the burrowers live in family groups, they interact vocally with each other and defend a mutual territory. Pikas are diurnal and are active early and late in the day during hot weather. They feed on all sorts of plant material. As they do not hibernate, they make "haypiles" of dried vegetation which they collect and carry back to their homes to store for use during winter.
Hares
Hares, members of genus Lepus of family Leporidae, are medium size mammals native to Europe, Asia, Africa, and North America. North American jackrabbits are actually hares. Species vary in size from in length and have long powerful back legs, and ears up to in length. Although usually greyish-brown, some species turn white in the winter. They are solitary animals. Newborns are precocial (eyes and ears open, fully furred). Several litters are born during the year in a form (a nest above ground, usually under a bush). They are preyed upon by large mammalian carnivores and birds of prey.
Rabbits | Lagomorpha | Wikipedia | 435 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Rabbits, members of the Leporidae family (excluding Lepus (hares)) are generally much smaller than hares and include the rock hares and the hispid hare. They are native to Europe, parts of Africa, Central and Southern Asia, North America and much of South America. They inhabit both grassland and arid regions. They vary in size from and have long, powerful hind legs, shorter forelegs and a tiny tail. The colour is some shade of brown, buff or grey and there is one black species and two striped ones. Domestic rabbits come in a wider variety of colours. Newborn rabbits are altricial (eyes and ears closed, no fur). Although most species live in burrows, the cottontails and hispid hares have forms (nests above ground, usually under a bush). Most of the burrowing species are colonial, and feed together in small groups. Rabbits play an important part in the terrestrial food chain, eating a wide range of forbs, grasses, and herbs, and being part of the staple diet of many carnivorous species. Domestic rabbits can be litter box trained, and—assuming they are given sufficient room to run and a good diet—can live long lives as house pets.
Distribution
Lagomorphs are widespread around the world and inhabit every continent except Antarctica. However, they are not found in most of the southern cone of South America, in the West Indies, Indonesia or Madagascar, nor on many islands. Although they are not native to Australia, humans have introduced them there and they have successfully colonized many parts of the country and caused disruption to native species.
Biology
Digestion
Easily digestible food is processed in the gastrointestinal tract and expelled as regular feces. But in order to get nutrients out of hard to digest fiber, lagomorphs ferment fiber in the cecum (in the GI tract) and then expel the contents as cecotropes, which are reingested (cecotrophy). The cecotropes are then absorbed in the small intestine to utilize the nutrients.
Like rodents, they are not able to vomit. | Lagomorpha | Wikipedia | 437 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Birth and early life
Many lagomorphs breed several times a year and produce large litters. This is particularly the case in species that live in underground, protective environments, such as burrows. The young of rabbits and pikas (called kits) are born after a short gestation period and the mother can become pregnant again almost immediately after giving birth. The mothers are able to leave these young safely and go off to feed, returning at intervals to feed them with their unusually rich milk. In some species, the mother only visits and feeds the litter once a day but the young grow rapidly and are usually weaned within a month.
Hare young are called leverets. Adults have a strategy to prevent predators from tracking down their litter by following the adults' scent. They approach and depart from the nesting site in a series of immense bounds, sometimes moving at right angles to their previous direction. Each litter of hares have a small number of young and are born after a longer gestation period.
Sociality and safety
Many species of lagomorphs, particularly the rabbits and the pikas, are gregarious and live in colonies, whereas hares are generally solitary species, although many hares travel and forage in groups of two, three, or four. Many rabbits and pikas rely on their burrows as places of safety when danger threatens, but hares rely on their long legs, great speed and jinking gait to escape from predators.
Classification
Recent genera
Order Lagomorpha Brandt 1885
Family Leporidae Fischer de Waldheim 1817 (rabbits and hares)
Subfamily Leporinae Trouessart 1880
Genus Brachylagus
Genus Bunolagus
Genus Caprolagus Blyth 1845
Genus Lepus Linnaeus 1758 (hare)
Genus Nesolagus Forsyth Major 1899
Genus Oryctolagus Lilljeborg 1874
Genus Pentalagus Lyon 1904
Genus Poelagus
Genus Pronolagus Lyon 1904
Genus Romerolagus Merriam 1896
Genus Sylvilagus Gray 1867
Family Ochotonidae Thomas 1897 (pikas)
Genus Ochotona Link 1795
Genus †Prolagus Pomel 1853 (considered by some sources to be the sole member of the family Prolagidae) | Lagomorpha | Wikipedia | 449 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Fossil genera
Order Lagomorpha Brandt 1885
Family Leporidae Fischer de Waldheim 1817 (rabbits and hares)
Subfamily † Archaeolaginae
Genus †Archaeolagus Dice 1917
Genus †Hypolagus Dice 1917
Genus †Notolagus Wilson 1938
Genus †Panolax Cope 1874
Subfamily Leporinae Trouessart 1880
Genus †Alilepus Dice 1931
Genus †Nuralagus Lilljeborg 1874
Genus †Pliolagus Kormos 1934
Genus †Pliosiwalagus Patnaik 2001
Genus †Pratilepus Hibbard 1939
Genus †Serengetilagus Dietrich 1941
Subfamily †Palaeolaginae Dice 1929
Tribe †Dasyporcina Gray 1825
Genus †Coelogenys Illiger 1811
Genus †Agispelagus Argyropulo 1939
Genus †Aluralagus Downey 1968
Genus †Austrolagomys Stromer 1926
Genus †Aztlanolagus Russell & Harris 1986
Genus †Chadrolagus Gawne 1978
Genus †Gobiolagus Burke 1941
Genus †Lagotherium Pictet 1853
Genus †Lepoides White 1988
Genus †Nekrolagus Hibbard 1939
Genus †Ordolagus de Muizon 1977
Genus †Paranotolagus Miller & Carranza-Castaneda 1982
Genus †Pewelagus White 1984
Genus †Pliopentalagus Gureev & Konkova 1964
Genus †Pronotolagus White 1991
Genus †Tachylagus Storer 1992
Genus †Trischizolagus Radulesco & Samson 1967
Genus †Veterilepus Radulesco & Samson 1967
Tribe incertae sedis
Genus †Litolagus Dawson 1958
Genus †Megalagus Walker 1931
Genus †Mytonolagus Burke 1934
Genus †Palaeolagus Leidy 1856
Family Ochotonidae Thomas 1897 (pikas)
Genus †Alloptox Dawson 1961
Genus †Amphilagus Tobien 1974
Genus †Bellatona Dawson 1961
Genus †Cuyamalagus Hutchison & Lindsay 1974
Genus †Desmatolagus Matthew & Granger 1923
Genus †Gripholagomys Green 1972
Genus †Hesperolagomys Clark et al. 1964
Genus †Kenyalagomys MacInnes 1953
Genus †Lagopsis Schlosser 1894
Genus †Ochotonoides Teilhard de Jardin & Young 1931
Genus †Ochotonoma Sen 1998
Genus †Oklahomalagus Dalquest et al. 1996
Genus †Oreolagus Dice 1917 | Lagomorpha | Wikipedia | 506 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
Genus †Piezodus Viret 1929
Genus †Russellagus Storer 1970
Genus †Sinolagomys Bohlin 1937
Genus †Titanomys von Meyer 1843
Family incertae sedis
Genus †Eurolagus Lopez Martinez 1977
Genus †Hsiuannania Xu 1976
Genus †Hypsimylus Zhai 1977
Genus †Lushilagus Li 1965
Genus †Shamolagus Burke 1941 | Lagomorpha | Wikipedia | 80 | 48317 | https://en.wikipedia.org/wiki/Lagomorpha | Biology and health sciences | Lagomorphs | null |
The retina (; or retinas) is the innermost, light-sensitive layer of tissue of the eye of most vertebrates and some molluscs. The optics of the eye create a focused two-dimensional image of the visual world on the retina, which then processes that image within the retina and sends nerve impulses along the optic nerve to the visual cortex to create visual perception. The retina serves a function which is in many ways analogous to that of the film or image sensor in a camera.
The neural retina consists of several layers of neurons interconnected by synapses and is supported by an outer layer of pigmented epithelial cells. The primary light-sensing cells in the retina are the photoreceptor cells, which are of two types: rods and cones. Rods function mainly in dim light and provide monochromatic vision. Cones function in well-lit conditions and are responsible for the perception of colour through the use of a range of opsins, as well as high-acuity vision used for tasks such as reading. A third type of light-sensing cell, the photosensitive ganglion cell, is important for entrainment of circadian rhythms and reflexive responses such as the pupillary light reflex.
Light striking the retina initiates a cascade of chemical and electrical events that ultimately trigger nerve impulses that are sent to various visual centres of the brain through the fibres of the optic nerve. Neural signals from the rods and cones undergo processing by other neurons, whose output takes the form of action potentials in retinal ganglion cells whose axons form the optic nerve.
In vertebrate embryonic development, the retina and the optic nerve originate as outgrowths of the developing brain, specifically the embryonic diencephalon; thus, the retina is considered part of the central nervous system (CNS) and is actually brain tissue. It is the only part of the CNS that can be visualized noninvasively. Like most of the brain, the retina is isolated from the vascular system by the blood–brain barrier. The retina is the part of the body with the greatest continuous energy demand.
Structure | Retina | Wikipedia | 450 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Inverted versus non-inverted retina
The vertebrate retina is inverted in the sense that the light-sensing cells are in the back of the retina, so that light has to pass through layers of neurons and capillaries before it reaches the photosensitive sections of the rods and cones. The ganglion cells, whose axons form the optic nerve, are at the front of the retina; therefore, the optic nerve must cross through the retina en route to the brain. No photoreceptors are in this region, giving rise to the blind spot. In contrast, in the cephalopod retina, the photoreceptors are in front, with processing neurons and capillaries behind them. Because of this, cephalopods do not have a blind spot.
Although the overlying neural tissue is partly transparent, and the accompanying glial cells have been shown to act as fibre-optic channels to transport photons directly to the photoreceptors, light scattering does occur. Some vertebrates, including humans, have an area of the central retina adapted for high-acuity vision. This area, termed the fovea centralis, is avascular (does not have blood vessels), and has minimal neural tissue in front of the photoreceptors, thereby minimizing light scattering.
The cephalopods have a non-inverted retina, which is comparable in resolving power to the eyes of many vertebrates. Squid eyes do not have an analog of the vertebrate retinal pigment epithelium (RPE). Although their photoreceptors contain a protein, retinochrome, that recycles retinal and replicates one of the functions of the vertebrate RPE, cephalopod photoreceptors are likely not maintained as well as in vertebrates, and that as a result, the useful lifetime of photoreceptors in invertebrates is much shorter than in vertebrates. Having easily replaced stalk eyes (some lobsters) or retinae (some spiders, such as Deinopis) rarely occurs. | Retina | Wikipedia | 443 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The cephalopod retina does not originate as an outgrowth of the brain, as the vertebrate one does. This difference suggests that vertebrate and cephalopod eyes are not homologous, but have evolved separately. From an evolutionary perspective, a more complex structure such as the inverted retina can generally come about as a consequence of two alternate processes - an advantageous "good" compromise between competing functional limitations, or as a historical maladaptive relic of the convoluted path of organ evolution and transformation. Vision is an important adaptation in higher vertebrates.
A third view of the "inverted" vertebrate eye is that it combines two benefits - the maintenance of the photoreceptors mentioned above, and the reduction in light intensity necessary to avoid blinding the photoreceptors, which are based on the extremely sensitive eyes of the ancestors of modern hagfish (fish that live in very deep, dark water).
A recent study on the evolutionary purpose for the inverted retina structure from the APS (American Physical Society) says that "The directional of glial cells helps increase the clarity of human vision. But we also noticed something rather curious: the colours that best passed through the glial cells were green to red, which the eye needs most for daytime vision. The eye usually receives too much blue—and thus has fewer blue-sensitive cones.
Further computer simulations showed that green and red are concentrated five to ten times more by the glial cells, and into their respective cones, than blue light. Instead, excess blue light gets scattered to the surrounding rods. This optimization is such that color vision during the day is enhanced, while night-time vision suffers very little".
Retinal layers
The vertebrate retina has 10 distinct layers. From closest to farthest from the vitreous body: | Retina | Wikipedia | 381 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Inner limiting membrane – basement membrane elaborated by Müller cells
Nerve fibre layer – axons of the ganglion cell bodies (a thin layer of Müller cell footplates exists between this layer and the inner limiting membrane)
Ganglion cell layer – contains nuclei of ganglion cells, the axons of which become the optic nerve fibres, and some displaced amacrine cells
Inner plexiform layer – contains the synapse between the bipolar cell axons and the dendrites of the ganglion and amacrine cells
Inner nuclear layer – contains the nuclei and surrounding cell bodies (perikarya) of the amacrine cells, bipolar cells, and horizontal cells
Outer plexiform layer – projections of rods and cones ending in the rod spherule and cone pedicle, respectively, these make synapses with dendrites of bipolar cells and horizontal cells. In the macular region, this is known as the Fiber layer of Henle.
Outer nuclear layer – cell bodies of rods and cones
External limiting membrane – layer that separates the inner segment portions of the photoreceptors from their cell nuclei
Inner segment / outer segment layer – inner segments and outer segments of rods and cones, the outer segments contain a highly specialized light-sensing apparatus.
Retinal pigment epithelium – single layer of cuboidal epithelial cells (with extrusions not shown in diagram). This layer is closest to the choroid, and provides nourishment and supportive functions to the neural retina, The black pigment melanin in the pigment layer prevents light reflection throughout the globe of the eyeball; this is extremely important for clear vision.
These layers can be grouped into four main processing stages—photoreception; transmission to bipolar cells; transmission to ganglion cells, which also contain photoreceptors, the photosensitive ganglion cells; and transmission along the optic nerve. At each synaptic stage, horizontal and amacrine cells also are laterally connected.
The optic nerve is a central tract of many axons of ganglion cells connecting primarily to the lateral geniculate body, a visual relay station in the diencephalon (the rear of the forebrain). It also projects to the superior colliculus, the suprachiasmatic nucleus, and the nucleus of the optic tract. It passes through the other layers, creating the optic disc in primates. | Retina | Wikipedia | 490 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Additional structures, not directly associated with vision, are found as outgrowths of the retina in some vertebrate groups. In birds, the pecten is a vascular structure of complex shape that projects from the retina into the vitreous humour; it supplies oxygen and nutrients to the eye, and may also aid in vision. Reptiles have a similar, but much simpler, structure.
In adult humans, the entire retina is about 72% of a sphere about 22 mm in diameter. The entire retina contains about 7 million cones and 75 to 150 million rods. The optic disc, a part of the retina sometimes called "the blind spot" because it lacks photoreceptors, is located at the optic papilla, where the optic-nerve fibres leave the eye. It appears as an oval white area of 3 mm2. Temporal (in the direction of the temples) to this disc is the macula, at whose centre is the fovea, a pit that is responsible for sharp central vision, but is actually less sensitive to light because of its lack of rods. Human and non-human primates possess one fovea, as opposed to certain bird species, such as hawks, that are bifoviate, and dogs and cats, that possess no fovea, but a central band known as the visual streak. Around the fovea extends the central retina for about 6 mm and then the peripheral retina. The farthest edge of the retina is defined by the ora serrata. The distance from one ora to the other (or macula), the most sensitive area along the horizontal meridian, is about 32 mm.
In section, the retina is no more than 0.5 mm thick. It has three layers of nerve cells and two of synapses, including the unique ribbon synapse. The optic nerve carries the ganglion-cell axons to the brain, and the blood vessels that supply the retina. The ganglion cells lie innermost in the eye while the photoreceptive cells lie beyond. Because of this counter-intuitive arrangement, light must first pass through and around the ganglion cells and through the thickness of the retina, (including its capillary vessels, not shown) before reaching the rods and cones. Light is absorbed by the retinal pigment epithelium or the choroid (both of which are opaque). | Retina | Wikipedia | 498 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The white blood cells in the capillaries in front of the photoreceptors can be perceived as tiny bright moving dots when looking into blue light. This is known as the blue field entoptic phenomenon (or Scheerer's phenomenon).
Between the ganglion-cell layer and the rods and cones are two layers of neuropils, where synaptic contacts are made. The neuropil layers are the outer plexiform layer and the inner plexiform layer. In the outer neuropil layer, the rods and cones connect to the vertically running bipolar cells, and the horizontally oriented horizontal cells connect to ganglion cells.
The central retina predominantly contains cones, while the peripheral retina predominantly contains rods. In total, the retina has about seven million cones and a hundred million rods. At the centre of the macula is the foveal pit where the cones are narrow and long, and arranged in a hexagonal mosaic, the most dense, in contradistinction to the much fatter cones located more peripherally in the retina. At the foveal pit, the other retinal layers are displaced, before building up along the foveal slope until the rim of the fovea, or parafovea, is reached, which is the thickest portion of the retina. The macula has a yellow pigmentation, from screening pigments, and is known as the macula lutea. The area directly surrounding the fovea has the highest density of rods converging on single bipolar cells. Since its cones have a much lesser convergence of signals, the fovea allows for the sharpest vision the eye can attain. | Retina | Wikipedia | 350 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Though the rod and cones are a mosaic of sorts, transmission from receptors, to bipolars, to ganglion cells is not direct. Since about 150 million receptors and only 1 million optic nerve fibres exist, convergence and thus mixing of signals must occur. Moreover, the horizontal action of the horizontal and amacrine cells can allow one area of the retina to control another (e.g. one stimulus inhibiting another). This inhibition is key to lessening the sum of messages sent to the higher regions of the brain. In some lower vertebrates (e.g. the pigeon), control of messages is "centrifugal" – that is, one layer can control another, or higher regions of the brain can drive the retinal nerve cells, but in primates, this does not occur.
Layers imagable with optical coherence tomography
Using optical coherence tomography (OCT), 18 layers can be identified in the retina. The layers and anatomical correlation are:
From innermost to outermost, the layers identifiable by OCT are as follows:
Development
Retinal development begins with the establishment of the eye fields mediated by the SHH and SIX3 proteins, with subsequent development of the optic vesicles regulated by the PAX6 and LHX2 proteins. The role of Pax6 in eye development was elegantly demonstrated by Walter Gehring and colleagues, who showed that ectopic expression of Pax6 can lead to eye formation on Drosophila antennae, wings, and legs. The optic vesicle gives rise to three structures: the neural retina, the retinal pigmented epithelium, and the optic stalk. The neural retina contains the retinal progenitor cells (RPCs) that give rise to the seven cell types of the retina. Differentiation begins with the retinal ganglion cells and concludes with production of the Muller glia. Although each cell type differentiates from the RPCs in a sequential order, there is considerable overlap in the timing of when individual cell types differentiate. The cues that determine a RPC daughter cell fate are coded by multiple transcription factor families including the bHLH and homeodomain factors. | Retina | Wikipedia | 457 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
In addition to guiding cell fate determination, cues exist in the retina to determine the dorsal-ventral (D-V) and nasal-temporal (N-T) axes. The D-V axis is established by a ventral to dorsal gradient of VAX2, whereas the N-T axis is coordinated by expression of the forkhead transcription factors FOXD1 and FOXG1. Additional gradients are formed within the retina. This spatial distribution may aid in proper targeting of RGC axons that function to establish the retinotopic map.
Blood supply
The retina is stratified into distinct layers, each containing specific cell types or cellular compartments that have metabolisms with different nutritional requirements. To satisfy these requirements, the ophthalmic artery bifurcates and supplies the retina via two distinct vascular networks: the choroidal network, which supplies the choroid and the outer retina, and the retinal network, which supplies the retina's inner layer.
Although the inverted retina of vertebrates appears counter-intuitive, it is necessary for the proper functioning of the retina. The photoreceptor layer must be embedded in the retinal pigment epithelium (RPE), which performs at least seven vital functions, one of the most obvious being to supply oxygen and other necessary nutrients needed for the photoreceptors to function.
Energy requirements
The energy requirements of the retina are even greater than that of the brain. This is due to the additional energy needed to continuously renew the photoreceptor outer segments, of which 10% are shed daily. Energy demands are greatest during dark adaptation when its sensitivity is most enhanced. The choroid supplies about 75% of these nutrients to the retina and the retinal vasculature only 25%. | Retina | Wikipedia | 372 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
When light strikes 11-cis-retinal (in the disks in the rods and cones), 11-cis-retinal changes to all-trans-retinal which then triggers changes in the opsins. Now, the outer segments do not regenerate the retinal back into the cis- form once it has been changed by light. Instead the retinal is pumped out to the surrounding RPE where it is regenerated and transported back into the outer segments of the photoreceptors. This recycling function of the RPE protects the photoreceptors against photo-oxidative damage and allows the photoreceptor cells to have decades-long useful lives.
In birds
The bird retina is devoid of blood vessels, perhaps to give unobscured passage of light for forming images, thus giving better resolution. It is, therefore, a considered view that the bird retina depends for nutrition and oxygen supply on a specialized organ, called the "pecten" or pecten oculi, located on the blind spot or optic disk. This organ is extremely rich in blood vessels and is thought to supply nutrition and oxygen to the bird retina by diffusion through the vitreous body. The pecten is highly rich in alkaline phosphatase activity and polarized cells in its bridge portion – both befitting its secretory role. Pecten cells are packed with dark melanin granules, which have been theorized to keep this organ warm with the absorption of stray light falling on the pecten. This is considered to enhance metabolic rate of the pecten, thereby exporting more nutritive molecules to meet the stringent energy requirements of the retina during long periods of exposure to light.
Biometric identification and diagnosis of disease | Retina | Wikipedia | 372 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The bifurcations and other physical characteristics of the inner retinal vascular network are known to vary among individuals, and these individual variances have been used for biometric identification and for early detection of the onset of disease. The mapping of vascular bifurcations is one of the basic steps in biometric identification. Results of such analyses of retinal blood vessel structure can be evaluated against the ground truth data of vascular bifurcations of retinal fundus images that are obtained from the DRIVE dataset. In addition, the classes of vessels of the DRIVE dataset have also been identified, and an automated method for accurate extraction of these bifurcations is also available. Changes in retinal blood circulation are seen with aging and exposure to air pollution, and may indicate cardiovascular diseases such as hypertension and atherosclerosis. Determining the equivalent width of arterioles and venules near the optic disc is also a widely used technique to identify cardiovascular risks.
Function
The retina translates an optical image into neural impulses starting with the patterned excitation of the colour-sensitive pigments of its rods and cones, the retina's photoreceptor cells. The excitation is processed by the neural system and various parts of the brain working in parallel to form a representation of the external environment in the brain.
The cones respond to bright light and mediate high-resolution colour vision during daylight illumination (also called photopic vision). The rod responses are saturated at daylight levels and do not contribute to pattern vision. However, rods do respond to dim light and mediate lower-resolution, monochromatic vision under very low levels of illumination (called scotopic vision). The illumination in most office settings falls between these two levels and is called mesopic vision. At mesopic light levels, both the rods and cones are actively contributing pattern information. What contribution the rod information makes to pattern vision under these circumstances is unclear. | Retina | Wikipedia | 401 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The response of cones to various wavelengths of light is called their spectral sensitivity. In normal human vision, the spectral sensitivity of a cone falls into one of three subtypes, often called blue, green, and red, but more accurately known as short, medium, and long wavelength-sensitive cone subtypes. It is a lack of one or more of the cone subtypes that causes individuals to have deficiencies in colour vision or various kinds of colour blindness. These individuals are not blind to objects of a particular colour, but are unable to distinguish between colours that can be distinguished by people with normal vision. Humans have this trichromatic vision, while most other mammals lack cones with red sensitive pigment and therefore have poorer dichromatic colour vision. However, some animals have four spectral subtypes, e.g. the trout adds an ultraviolet subgroup to short, medium, and long subtypes that are similar to humans. Some fish are sensitive to the polarization of light as well.
In the photoreceptors, exposure to light hyperpolarizes the membrane in a series of graded shifts. The outer cell segment contains a photopigment. Inside the cell the normal levels of cyclic guanosine monophosphate (cGMP) keep the Na+ channel open, and thus in the resting state the cell is depolarised. The photon causes the retinal bound to the receptor protein to isomerise to trans-retinal. This causes the receptor to activate multiple G-proteins. This in turn causes the Ga-subunit of the protein to activate a phosphodiesterase (PDE6), which degrades cGMP, resulting in the closing of Na+ cyclic nucleotide-gated ion channels (CNGs). Thus the cell is hyperpolarised. The amount of neurotransmitter released is reduced in bright light and increases as light levels fall. The actual photopigment is bleached away in bright light and only replaced as a chemical process, so in a transition from bright light to darkness the eye can take up to thirty minutes to reach full sensitivity. | Retina | Wikipedia | 442 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
When thus excited by light, the photoceptor sends a proportional response synaptically to bipolar cells which in turn signal the retinal ganglion cells. The photoreceptors are also cross-linked by horizontal cells and amacrine cells, which modify the synaptic signal before it reaches the ganglion cells, the neural signals being intermixed and combined. Of the retina's nerve cells, only the retinal ganglion cells and few amacrine cells create action potentials.
In the retinal ganglion cells there are two types of response, depending on the receptive field of the cell. The receptive fields of retinal ganglion cells comprise a central, approximately circular area, where light has one effect on the firing of the cell, and an annular surround, where light has the opposite effect. In ON cells, an increment in light intensity in the centre of the receptive field causes the firing rate to increase. In OFF cells, it makes it decrease. In a linear model, this response profile is well described by a difference of Gaussians and is the basis for edge detection algorithms. Beyond this simple difference, ganglion cells are also differentiated by chromatic sensitivity and the type of spatial summation. Cells showing linear spatial summation are termed X cells (also called parvocellular, P, or midget ganglion cells), and those showing non-linear summation are Y cells (also called magnocellular, M, or parasol retinal ganglion cells), although the correspondence between X and Y cells (in the cat retina) and P and M cells (in the primate retina) is not as simple as it once seemed.
In the transfer of visual signals to the brain, the visual pathway, the retina is vertically divided in two, a temporal (nearer to the temple) half and a nasal (nearer to the nose) half. The axons from the nasal half cross the brain at the optic chiasma to join with axons from the temporal half of the other eye before passing into the lateral geniculate body. | Retina | Wikipedia | 435 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Although there are more than 130 million retinal receptors, there are only approximately 1.2 million fibres (axons) in the optic nerve. So, a large amount of pre-processing is performed within the retina. The fovea produces the most accurate information. Despite occupying about 0.01% of the visual field (less than 2° of visual angle), about 10% of axons in the optic nerve are devoted to the fovea. The resolution limit of the fovea has been determined to be around 10,000 points. The information capacity is estimated at 500,000 bits per second (for more information on bits, see information theory) without colour or around 600,000 bits per second including colour.
Spatial encoding
When the retina sends neural impulses representing an image to the brain, it spatially encodes (compresses) those impulses to fit the limited capacity of the optic nerve. Compression is necessary because there are 100 times more photoreceptor cells than ganglion cells. This is done by "decorrelation", which is carried out by the "centre–surround structures", which are implemented by the bipolar and ganglion cells.
There are two types of centre–surround structures in the retina – on-centres and off-centres. On-centres have a positively weighted centre and a negatively weighted surround. Off-centres are just the opposite. Positive weighting is more commonly known as excitatory, and negative weighting as inhibitory.
These centre–surround structures are not physical apparent, in the sense that one cannot see them by staining samples of tissue and examining the retina's anatomy. The centre–surround structures are logical (i.e., mathematically abstract) in the sense that they depend on the connection strengths between bipolar and ganglion cells. It is believed that the connection strength between cells is caused by the number and types of ion channels embedded in the synapses between the bipolar and ganglion cells. | Retina | Wikipedia | 409 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The centre–surround structures are mathematically equivalent to the edge detection algorithms used by computer programmers to extract or enhance the edges in a digital photograph. Thus, the retina performs operations on the image-representing impulses to enhance the edges of objects within its visual field. For example, in a picture of a dog, a cat and a car, it is the edges of these objects that contain the most information. In order for higher functions in the brain (or in a computer for that matter) to extract and classify objects such as a dog and a cat, the retina is the first step to separating out the various objects within the scene.
As an example, the following matrix is at the heart of a computer algorithm that implements edge detection. This matrix is the computer equivalent to the centre–surround structure. In this example, each box (element) within this matrix would be connected to one photoreceptor. The photoreceptor in the centre is the current receptor being processed. The centre photoreceptor is multiplied by the +1 weight factor. The surrounding photoreceptors are the "nearest neighbors" to the centre and are multiplied by the −1/8 value. The sum of all nine of these elements is finally calculated. This summation is repeated for every photoreceptor in the image by shifting left to the end of a row and then down to the next line.
The total sum of this matrix is zero, if all the inputs from the nine photoreceptors are of the same value. The zero result indicates the image was uniform (non-changing) within this small patch. Negative or positive sums mean the image was varying (changing) within this small patch of nine photoreceptors. | Retina | Wikipedia | 358 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The above matrix is only an approximation to what really happens inside the retina. The differences are:
The above example is called "balanced". The term balanced means that the sum of the negative weights is equal to the sum of the positive weights so that they cancel out perfectly. Retinal ganglion cells are almost never perfectly balanced.
The table is square while the centre–surround structures in the retina are circular.
Neurons operate on spike trains traveling down nerve cell axons. Computers operate on a single floating-point number that is essentially constant from each input pixel. (The computer pixel is basically the equivalent of a biological photoreceptor.)
The retina performs all these calculations in parallel while the computer operates on each pixel one at a time. The retina performs no repeated summations and shifting as would a computer.
Finally, the horizontal and amacrine cells play a significant role in this process, but that is not represented here.
Here is an example of an input image and how edge detection would modify it.
Once the image is spatially encoded by the centre–surround structures, the signal is sent out along the optic nerve (via the axons of the ganglion cells) through the optic chiasm to the LGN (lateral geniculate nucleus). The exact function of the LGN is unknown at this time. The output of the LGN is then sent to the back of the brain. Specifically, the output of the LGN "radiates" out to the V1 primary visual cortex.
Simplified signal flow: Photoreceptors → Bipolar → Ganglion → Chiasm → LGN → V1 cortex | Retina | Wikipedia | 337 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Clinical significance
There are many inherited and acquired diseases or disorders that may affect the retina. Some of them include:
Retinitis pigmentosa is a group of genetic diseases that affect the retina and cause the loss of night vision and peripheral vision.
Macular degeneration describes a group of diseases characterized by loss of central vision because of death or impairment of the cells in the macula.
Cone-rod dystrophy (CORD) describes a number of diseases where vision loss is caused by deterioration of the cones and/or rods in the retina.
In retinal separation, the retina detaches from the back of the eyeball. Ignipuncture is an outdated treatment method. The term retinal detachment is used to describe a separation of the neurosensory retina from the retinal pigment epithelium. There are several modern treatment methods for fixing a retinal detachment: pneumatic retinopexy, scleral buckle, cryotherapy, laser photocoagulation and pars plana vitrectomy.
Both hypertension and diabetes mellitus can cause damage to the tiny blood vessels that supply the retina, leading to hypertensive retinopathy and diabetic retinopathy.
Retinoblastoma is a cancer of the retina.
Retinal diseases in dogs include retinal dysplasia, progressive retinal atrophy, and sudden acquired retinal degeneration.
Lipaemia retinalis is a white appearance of the retina, and can occur by lipid deposition in lipoprotein lipase deficiency.
Retinal Detachment. The neural retina occasionally detaches from the pigment epithelium. In some instances, the cause of such detachment is injury to the eyeball that allows fluid or blood to collect between the neural retina and the pigment epithelium. Detachment is occasionally caused by contracture of fine collagenous fibrils in the vitreous humor, which pull areas of the retina toward the interior of the globe.
Night blindness: Night blindness occurs in any person with severe vitamin A deficiency. The reason for this is that without vitamin A, the amounts of retinal and rhodopsin that can be formed are severely depressed. This condition is called night blindness because the amount of light available at night is too little to permit adequate vision in vitamin A–deficient persons. | Retina | Wikipedia | 503 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
In addition, the retina has been described as a "window" into the brain and body, given that abnormalities detected through an examination of the retina can discover both neurological and systemic diseases.
Diagnosis
A number of different instruments are available for the diagnosis of diseases and disorders affecting the retina. Ophthalmoscopy and fundus photography have long been used to examine the retina. Recently, adaptive optics has been used to image individual rods and cones in the living human retina, and a company based in Scotland has engineered technology that allows physicians to observe the complete retina without any discomfort to patients.
The electroretinogram is used to non-invasively measure the retina's electrical activity, which is affected by certain diseases. A relatively new technology, now becoming widely available, is optical coherence tomography (OCT). This non-invasive technique allows one to obtain a 3D volumetric or high resolution cross-sectional tomogram of the fine structures of the retina, with histologic quality. Retinal vessel analysis is a non-invasive method to examine the small arteries and veins in the retina which allows to draw conclusions about the morphology and the function of small vessels elsewhere in the human body. It has been established as a predictor of cardiovascular disease and seems to have, according to a study published in 2019, potential in the early detection of Alzheimer's disease.
Treatment
Treatment depends upon the nature of the disease or disorder.
Common treatment modalities
The following are commonly modalities of management for retinal disease:
Intravitreal medication, such as anti-VEGF or corticosteroid agents
Vitreoretinal surgery
Use of nutritional supplements
Modification of systemic risk factors for retinal disease
Uncommon treatment modalities
Retinal gene therapy | Retina | Wikipedia | 367 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Gene therapy holds promise as a potential avenue to cure a wide range of retinal diseases. This involves using a non-infectious virus to shuttle a gene into a part of the retina. Recombinant adeno-associated virus (rAAV) vectors possess a number of features that render them ideally suited for retinal gene therapy, including a lack of pathogenicity, minimal immunogenicity, and the ability to transduce postmitotic cells in a stable and efficient manner. rAAV vectors are increasingly utilized for their ability to mediate efficient transduction of retinal pigment epithelium (RPE), photoreceptor cells and retinal ganglion cells. Each cell type can be specifically targeted by choosing the appropriate combination of AAV serotype, promoter, and intraocular injection site.
Several clinical trials have already reported positive results using rAAV to treat Leber's congenital amaurosis, showing that the therapy was both safe and effective. There were no serious adverse events, and patients in all three studies showed improvement in their visual function as measured by a number of methods. The methods used varied among the three trials, but included both functional methods such as visual acuity and functional mobility as well as objective measures that are less susceptible to bias, such as the pupil's ability to respond to light and improvements on functional MRI. Improvements were sustained over the long-term, with patients continuing to do well after more than 1.5 years. | Retina | Wikipedia | 305 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
The unique architecture of the retina and its relatively immune-privileged environment help this process. Tight junctions that form the blood retinal barrier separate the subretinal space from the blood supply, thus protecting it from microbes and most immune-mediated damage, and enhancing its potential to respond to vector-mediated therapies. The highly compartmentalized anatomy of the eye facilitates accurate delivery of therapeutic vector suspensions to specific tissues under direct visualization using microsurgical techniques. In the sheltered environment of the retina, AAV vectors are able to maintain high levels of transgene expression in the retinal pigmented epithelium (RPE), photoreceptors, or ganglion cells for long periods of time after a single treatment. In addition, the eye and the visual system can be routinely and easily monitored for visual function and retinal structural changes after injections with noninvasive advanced technology, such as visual acuities, contrast sensitivity, fundus auto-fluorescence (FAF), dark-adapted visual thresholds, vascular diameters, pupillometry, electroretinography (ERG), multifocal ERG and optical coherence tomography (OCT). | Retina | Wikipedia | 252 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
This strategy is effective against a number of retinal diseases that have been studied, including neovascular diseases that are features of age-related macular degeneration, diabetic retinopathy and retinopathy of prematurity. Since the regulation of vascularization in the mature retina involves a balance between endogenous positive growth factors, such as vascular endothelial growth factor (VEGF) and inhibitors of angiogenesis, such as pigment epithelium-derived factor (PEDF), rAAV-mediated expression of PEDF, angiostatin, and the soluble VEGF receptor sFlt-1, which are all antiangiogenic proteins, have been shown to reduce aberrant vessel formation in animal models. Since specific gene therapies cannot readily be used to treat a significant fraction of patients with retinal dystrophy, there is a major interest in developing a more generally applicable survival factor therapy. Neurotrophic factors have the ability to modulate neuronal growth during development to maintain existing cells and to allow recovery of injured neuronal populations in the eye. AAV encoding neurotrophic factors such as fibroblast growth factor (FGF) family members and GDNF either protected photoreceptors from apoptosis or slowed down cell death.
Organ transplantation
Transplantation of retinas has been attempted, but without much success. At MIT, The University of Southern California, RWTH Aachen University, and the University of New South Wales, an "artificial retina" is under development: an implant which will bypass the photoreceptors of the retina and stimulate the attached nerve cells directly, with signals from a digital camera.
History
Around 300 BCE, Herophilos identified the retina from dissections of cadaver eyes. He called it the arachnoid layer, from its resemblance to a spider web, and retiform, from its resemblance to a casting net. The term arachnoid came to refer to a layer around the brain; the term retiform came to refer to the retina. | Retina | Wikipedia | 436 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
Between 1011 and 1021 CE, Ibn Al-Haytham published numerous experiments demonstrating that sight occurs from light reflecting from objects into the eye. This is consistent with intromission theory and against emission theory, the theory that sight occurs from rays emitted by the eyes. However, Ibn Al-Haytham decided that the retina could not be responsible for the beginnings of vision because the image formed on it was inverted. Instead he decided it must begin at the surface of the lens.
In 1604, Johannes Kepler worked out the optics of the eye and decided that the retina must be where sight begins. He left it up to other scientists to reconcile the inverted retinal image with our perception of the world as upright.
In 1894, Santiago Ramón y Cajal published the first major characterization of retinal neurons in Retina der Wirbelthiere (The Retina of Vertebrates).
George Wald, Haldan Keffer Hartline, and Ragnar Granit won the 1967 Nobel Prize in Physiology or Medicine for their scientific research on the retina.
A recent University of Pennsylvania study calculated that the approximate bandwidth of human retinas is 8.75 megabits per second, whereas a guinea pig's retinal transfer rate is 875 kilobits per second.
MacLaren & Pearson and colleagues at University College London and Moorfields Eye Hospital in London, in 2006, showed that photoreceptor cells could be transplanted successfully in the mouse retina if donor cells were at a critical developmental stage. Recently Ader and colleagues in Dublin showed, using the electron microscope, that transplanted photoreceptors formed synaptic connections.
In 2012, Sebastian Seung and his laboratory at MIT launched EyeWire, an online Citizen science game where players trace neurons in the retina. The goals of the EyeWire project are to identify specific cell types within the known broad classes of retinal cells, and to map the connections between neurons in the retina, which will help to determine how vision works.
Additional images | Retina | Wikipedia | 415 | 48334 | https://en.wikipedia.org/wiki/Retina | Biology and health sciences | Visual system | Biology |
An electrolyte is a substance that conducts electricity through the movement of ions, but not through the movement of electrons. This includes most soluble salts, acids, and bases, dissolved in a polar solvent like water. Upon dissolving, the substance separates into cations and anions, which disperse uniformly throughout the solvent. Solid-state electrolytes also exist. In medicine and sometimes in chemistry, the term electrolyte refers to the substance that is dissolved.
Electrically, such a solution is neutral. If an electric potential is applied to such a solution, the cations of the solution are drawn to the electrode that has an abundance of electrons, while the anions are drawn to the electrode that has a deficit of electrons. The movement of anions and cations in opposite directions within the solution amounts to a current. Some gases, such as hydrogen chloride (HCL), under conditions of high temperature or low pressure can also function as electrolytes. Electrolyte solutions can also result from the dissolution of some biological (e.g., DNA, polypeptides) or synthetic polymers (e.g., polystyrene sulfonate), termed "polyelectrolytes", which contain charged functional groups. A substance that dissociates into ions in solution or in the melt acquires the capacity to conduct electricity. Sodium, potassium, chloride, calcium, magnesium, and phosphate in a liquid phase are examples of electrolytes.
In medicine, electrolyte replacement is needed when a person has prolonged vomiting or diarrhea, and as a response to sweating due to strenuous athletic activity. Commercial electrolyte solutions are available, particularly for sick children (such as oral rehydration solution, Suero Oral, or Pedialyte) and athletes (sports drinks). Electrolyte monitoring is important in the treatment of anorexia and bulimia.
In science, electrolytes are one of the main components of electrochemical cells.
In clinical medicine, mentions of electrolytes usually refer metonymically to the ions, and (especially) to their concentrations (in blood, serum, urine, or other fluids). Thus, mentions of electrolyte levels usually refer to the various ion concentrations, not to the fluid volumes. | Electrolyte | Wikipedia | 468 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Etymology
The word electrolyte derives from Ancient Greek ήλεκτρο- (ēlectro-), prefix originally meaning amber but in modern contexts related to electricity, and λυτός (lytos), meaning "able to be untied or loosened".
History
In his 1884 dissertation, Svante Arrhenius put forth his explanation of solid crystalline salts disassociating into paired charged particles when dissolved, for which he won the 1903 Nobel Prize in Chemistry. Arrhenius's explanation was that in forming a solution, the salt dissociates into charged particles, to which Michael Faraday (1791-1867) had given the name "ions" many years earlier. Faraday's belief had been that ions were produced in the process of electrolysis. Arrhenius proposed that, even in the absence of an electric current, solutions of salts contained ions. He thus proposed that chemical reactions in solution were reactions between ions.
Shortly after Arrhenius's hypothesis of ions, Franz Hofmeister and Siegmund Lewith found that different ion types displayed different effects on such things as the solubility of proteins. A consistent ordering of these different ions on the magnitude of their effect arises consistently in many other systems as well. This has since become known as the Hofmeister series.
While the origins of these effects are not abundantly clear and have been debated throughout the past century, it has been suggested that the charge density of these ions is important and might actually have explanations originating from the work of Charles-Augustin de Coulomb over 200 years ago.
Formation
Electrolyte solutions are normally formed when salt is placed into a solvent such as water and the individual components dissociate due to the thermodynamic interactions between solvent and solute molecules, in a process called "solvation". For example, when table salt (sodium chloride), NaCl, is placed in water, the salt (a solid) dissolves into its component ions, according to the dissociation reaction:
NaCl(s) → Na+(aq) + Cl−(aq)
It is also possible for substances to react with water, producing ions. For example, carbon dioxide gas dissolves in water to produce a solution that contains hydronium, carbonate, and hydrogen carbonate ions. | Electrolyte | Wikipedia | 482 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Molten salts can also be electrolytes as, for example, when sodium chloride is molten, the liquid conducts electricity. In particular, ionic liquids, which are molten salts with melting points below 100 °C, are a type of highly conductive non-aqueous electrolytes and thus have found more and more applications in fuel cells and batteries.
An electrolyte in a solution may be described as "concentrated" if it has a high concentration of ions, or "dilute" if it has a low concentration. If a high proportion of the solute dissociates to form free ions, the electrolyte is strong; if most of the solute does not dissociate, the electrolyte is weak. The properties of electrolytes may be exploited using electrolysis to extract constituent elements and compounds contained within the solution.
Alkaline earth metals form hydroxides that are strong electrolytes with limited solubility in water, due to the strong attraction between their constituent ions. This limits their application to situations where high solubility is required.
In 2021, researchers have found that electrolyte can "substantially facilitate electrochemical corrosion studies in less conductive media".
Physiological importance
In physiology, the primary ions of electrolytes are sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), chloride (Cl−), hydrogen phosphate (HPO42−), and hydrogen carbonate (HCO3−). The electric charge symbols of plus (+) and minus (−) indicate that the substance is ionic in nature and has an imbalanced distribution of electrons, the result of chemical dissociation. Sodium is the main electrolyte found in extracellular fluid and potassium is the main intracellular electrolyte; both are involved in fluid balance and blood pressure control.
All known multicellular lifeforms require a subtle and complex electrolyte balance between the intracellular and extracellular environments. In particular, the maintenance of precise osmotic gradients of electrolytes is important. Such gradients affect and regulate the hydration of the body as well as blood pH, and are critical for nerve and muscle function. Various mechanisms exist in living species that keep the concentrations of different electrolytes under tight control. | Electrolyte | Wikipedia | 471 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Both muscle tissue and neurons are considered electric tissues of the body. Muscles and neurons are activated by electrolyte activity between the extracellular fluid or interstitial fluid, and intracellular fluid. Electrolytes may enter or leave the cell membrane through specialized protein structures embedded in the plasma membrane called "ion channels". For example, muscle contraction is dependent upon the presence of calcium (Ca2+), sodium (Na+), and potassium (K+). Without sufficient levels of these key electrolytes, muscle weakness or severe muscle contractions may occur.
Electrolyte balance is maintained by oral, or in emergencies, intravenous (IV) intake of electrolyte-containing substances, and is regulated by hormones, in general with the kidneys flushing out excess levels. In humans, electrolyte homeostasis is regulated by hormones such as antidiuretic hormones, aldosterone and parathyroid hormones. Serious electrolyte disturbances, such as dehydration and overhydration, may lead to cardiac and neurological complications and, unless they are rapidly resolved, will result in a medical emergency.
Measurement
Measurement of electrolytes is a commonly performed diagnostic procedure, performed via blood testing with ion-selective electrodes or urinalysis by medical technologists. The interpretation of these values is somewhat meaningless without analysis of the clinical history and is often impossible without parallel measurements of renal function. The electrolytes measured most often are sodium and potassium. Chloride levels are rarely measured except for arterial blood gas interpretations since they are inherently linked to sodium levels. One important test conducted on urine is the specific gravity test to determine the occurrence of an electrolyte imbalance.
Rehydration
According to a study paid for by the Gatorade Sports Science Institute, electrolyte drinks containing sodium and potassium salts replenish the body's water and electrolyte concentrations after dehydration caused by exercise, excessive alcohol consumption, diaphoresis (heavy sweating), diarrhea, vomiting, intoxication or starvation; the study says that athletes exercising in extreme conditions (for three or more hours continuously, e.g. a marathon or triathlon) who do not consume electrolytes risk dehydration (or hyponatremia). | Electrolyte | Wikipedia | 465 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
A home-made electrolyte drink can be made by using water, sugar and salt in precise proportions. It is important to include glucose (sugar) to utilise the co-transport mechanism of sodium and glucose. Commercial preparations are also available for both human and veterinary use.
Electrolytes are commonly found in fruit juices, sports drinks, milk, nuts, and many fruits and vegetables (whole or in juice form) (e.g., potatoes, avocados).
Electrochemistry
When electrodes are placed in an electrolyte and a voltage is applied, the electrolyte will conduct electricity. Lone electrons normally cannot pass through the electrolyte; instead, a chemical reaction occurs at the cathode, providing electrons to the electrolyte. Another reaction occurs at the anode, consuming electrons from the electrolyte. As a result, a negative charge cloud develops in the electrolyte around the cathode, and a positive charge develops around the anode. The ions in the electrolyte neutralize these charges, enabling the electrons to keep flowing and the reactions to continue.
For example, in a solution of ordinary table salt (sodium chloride, NaCl) in water, the cathode reaction will be
2 H2O + 2e− → 2 OH− + H2
and hydrogen gas will bubble up; the anode reaction is
2 NaCl → 2 Na+ + Cl2 + 2e−
and chlorine gas will be liberated into solution where it reacts with the sodium and hydroxyl ions to produce sodium hypochlorite - household bleach. The positively charged sodium ions Na+ will react toward the cathode, neutralizing the negative charge of OH− there, and the negatively charged hydroxide ions OH− will react toward the anode, neutralizing the positive charge of Na+ there. Without the ions from the electrolyte, the charges around the electrode would slow down continued electron flow; diffusion of H+ and OH− through water to the other electrode takes longer than movement of the much more prevalent salt ions.
Electrolytes dissociate in water because water molecules are dipoles and the dipoles orient in an energetically favorable manner to solvate the ions.
In other systems, the electrode reactions can involve the metals of the electrodes as well as the ions of the electrolyte. | Electrolyte | Wikipedia | 486 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Electrolytic conductors are used in electronic devices where the chemical reaction at a metal-electrolyte interface yields useful effects.
In batteries, two materials with different electron affinities are used as electrodes; electrons flow from one electrode to the other outside of the battery, while inside the battery the circuit is closed by the electrolyte's ions. Here, the electrode reactions convert chemical energy to electrical energy.
In some fuel cells, a solid electrolyte or proton conductor connects the plates electrically while keeping the hydrogen and oxygen fuel gases separated.
In electroplating tanks, the electrolyte simultaneously deposits metal onto the object to be plated, and electrically connects that object in the circuit.
In operation-hours gauges, two thin columns of mercury are separated by a small electrolyte-filled gap, and, as charge is passed through the device, the metal dissolves on one side and plates out on the other, causing the visible gap to slowly move along.
In electrolytic capacitors the chemical effect is used to produce an extremely thin dielectric or insulating coating, while the electrolyte layer behaves as one capacitor plate.
In some hygrometers the humidity of air is sensed by measuring the conductivity of a nearly dry electrolyte.
Hot, softened glass is an electrolytic conductor, and some glass manufacturers keep the glass molten by passing a large current through it.
Solid electrolytes
Solid electrolytes can be mostly divided into four groups described below.
Gel electrolytes
Gel electrolytes – closely resemble liquid electrolytes. In essence, they are liquids in a flexible lattice framework. Various additives are often applied to increase the conductivity of such systems.
Ceramic electrolytes
Solid ceramic electrolytes – ions migrate through the ceramic phase by means of vacancies or interstitials within the lattice. There are also glassy-ceramic electrolytes.
Polymer electrolytes | Electrolyte | Wikipedia | 398 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Dry polymer electrolytes differ from liquid and gel electrolytes in that salt is dissolved directly into the solid medium. Usually it is a relatively high-dielectric constant polymer (PEO, PMMA, PAN, polyphosphazenes, siloxanes, etc.) and a salt with low lattice energy. In order to increase the mechanical strength and conductivity of such electrolytes, very often composites are made, and inert ceramic phase is introduced. There are two major classes of such electrolytes: polymer-in-ceramic, and ceramic-in-polymer.
Organic plastic electrolytes
Organic ionic plastic crystals – are a type organic salts exhibiting mesophases (i.e. a state of matter intermediate between liquid and solid), in which mobile ions are orientationally or rotationally disordered while their centers are located at the ordered sites in the crystal structure. They have various forms of disorder due to one or more solid–solid phase transitions below the melting point and have therefore plastic properties and good mechanical flexibility as well as an improved electrode-electrolyte interfacial contact. In particular, protic organic ionic plastic crystals (POIPCs), which are solid protic organic salts formed by proton transfer from a Brønsted acid to a Brønsted base and in essence are protic ionic liquids in the molten state, have found to be promising solid-state proton conductors for fuel cells. Examples include 1,2,4-triazolium perfluorobutanesulfonate and imidazolium methanesulfonate. | Electrolyte | Wikipedia | 327 | 48336 | https://en.wikipedia.org/wiki/Electrolyte | Physical sciences | Electrochemistry | Chemistry |
Caterpillars ( ) are the larval stage of members of the order Lepidoptera (the insect order comprising butterflies and moths).
As with most common names, the application of the word is arbitrary, since the larvae of sawflies (suborder Symphyta) are commonly called caterpillars as well. Both lepidopteran and symphytan larvae have eruciform body shapes.
Caterpillars of most species eat plant material (often leaves), but not all; some (about 1%) eat insects, and some are even cannibalistic. Some feed on other animal products. For example, clothes moths feed on wool, and horn moths feed on the hooves and horns of dead ungulates.
Caterpillars are typically voracious feeders and many of them are among the most serious of agricultural pests. In fact, many moth species are best known in their caterpillar stages because of the damage they cause to fruits and other agricultural produce, whereas the moths are obscure and do no direct harm. Conversely, various species of caterpillar are valued as sources of silk, as human or animal food, or for biological control of pest plants.
Etymology
The origins of the word "caterpillar" date from the early 16th century. They derive from Middle English catirpel, catirpeller, probably an alteration of Old North French catepelose: cate, cat (from Latin cattus) + pelose, hairy (from Latin pilōsus).
The inchworm, or looper caterpillars from the family Geometridae are so named because of the way they move, appearing to measure the earth (the word geometrid means earth-measurer in Greek); the primary reason for this unusual locomotion is the elimination of nearly all the prolegs except the clasper on the terminal segment.
Description | Caterpillar | Wikipedia | 389 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Caterpillars have soft bodies that can grow rapidly between moults. Their size varies between species and instars (moults) from as small as up to . Some larvae of the order Hymenoptera (ants, bees, and wasps) can appear like the caterpillars of the Lepidoptera. Such larvae are mainly seen in the sawfly suborder. However while these larvae superficially resemble caterpillars, they can be distinguished by the presence of prolegs on every abdominal segment, an absence of crochets or hooks on the prolegs (these are present on lepidopteran caterpillars), one pair of prominent ocelli on the head capsule, and an absence of the upside-down Y-shaped suture on the front of the head.
Lepidopteran caterpillars can be differentiated from sawfly larvae by:
the numbers of pairs of pro-legs; sawfly larvae have 6 or more pairs while caterpillars have a maximum of 5 pairs.
the number of stemmata (simple eyes); the sawfly larvae have only two, while caterpillars usually have twelve (six each side of the head).
the presence of crochets on the prolegs; these are absent in the sawflies.
sawfly larvae have an invariably smooth head capsule with no cleavage lines, while lepidopterous caterpillars bear an inverted "Y" or "V" (frontal suture).
Fossils
In 2019, a geometrid moth caterpillar dating back to the Eocene epoch, approximately 44 million years ago, was found preserved in Baltic amber. It was described under Eogeometer vadens. Previously, another fossil dating back approximately 125 million years was found in Lebanese amber.
Defenses
Many animals feed on caterpillars as they are rich in protein. As a result, caterpillars have evolved various means of defense.
Caterpillars have evolved defenses against physical conditions such as cold, hot or dry environmental conditions. Some Arctic species like Gynaephora groenlandica have special basking and aggregation behaviours apart from physiological adaptations to remain in a dormant state.
Appearance | Caterpillar | Wikipedia | 455 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
The appearance of a caterpillar can often repel a predator: its markings and certain body parts can make it seem poisonous, or bigger in size and thus threatening, or non-edible. Some types of caterpillars are indeed poisonous or distasteful and their bright coloring warns predators of this. Others may mimic dangerous caterpillars or other animals while not being dangerous themselves. Many caterpillars are cryptically colored and resemble the plants on which they feed. An example of caterpillars that use camouflage for defense is the species Nemoria arizonaria. If the caterpillars hatch in the spring and feed on oak catkins they appear green. If they hatch in the summer they appear dark colored, like oak twigs. The differential development is linked to the tannin content in the diet. Caterpillars may even have spines or growths that resemble plant parts such as thorns. Some look like objects in the environment such as bird droppings. Some Geometridae cover themselves in plant parts, while bagworms construct and live in a bag covered in sand, pebbles or plant material.
Chemical defenses
More aggressive self-defense measures have evolved in some caterpillars. These measures include having spiny bristles or long fine hair-like setae with detachable tips that will irritate by lodging in the skin or mucous membranes. However some birds (such as cuckoos) will swallow even the hairiest of caterpillars. Other caterpillars acquire toxins from their host plants that render them unpalatable to most of their predators. For instance, ornate moth caterpillars utilize pyrrolizidine alkaloids that they obtain from their food plants to deter predators. The most aggressive caterpillar defenses are bristles associated with venom glands. These bristles are called urticating hairs. A venom which is among the most potent defensive chemicals in any animal is produced by the South American silk moth genus Lonomia. Its venom is an anticoagulant powerful enough to cause a human to hemorrhage to death (See Lonomiasis). This chemical is being investigated for potential medical applications. Most urticating hairs range in effect from mild irritation to dermatitis. Example: brown-tail moth. | Caterpillar | Wikipedia | 469 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Plants contain toxins which protect them from herbivores, but some caterpillars have evolved countermeasures which enable them to eat the leaves of such toxic plants. In addition to being unaffected by the poison, the caterpillars sequester it in their body, making them highly toxic to predators. The chemicals are also carried on into the adult stages. These toxic species, such as the cinnabar moth (Tyria jacobaeae) and monarch (Danaus plexippus) caterpillars, usually advertise themselves with the danger colors of red, yellow and black, often in bright stripes (see aposematism). Any predator that attempts to eat a caterpillar with an aggressive defense mechanism will learn and avoid future attempts.
Some caterpillars regurgitate acidic digestive juices at attacking enemies. Many papilionid larvae produce bad smells from extrudable glands called osmeteria.
Defensive behaviors
Many caterpillars display feeding behaviors which allow the caterpillar to remain hidden from potential predators. Many feed in protected environments, such as enclosed inside silk galleries, rolled leaves or by mining between the leaf surfaces.
Some caterpillars, like early instars of the tomato hornworm and tobacco hornworm, have long "whip-like" organs attached to the ends of their body. The caterpillar wiggles these organs to frighten away flies and predatory wasps. Some caterpillars can evade predators by using a silk line and dropping off from branches when disturbed. Many species thrash about violently when disturbed to scare away potential predators. One species (Amorpha juglandis) even makes high pitched whistles that can scare away birds.
Social behaviors and relationships with other insects
Some caterpillars obtain protection by associating themselves with ants. The Lycaenid butterflies are particularly well known for this. They communicate with their ant protectors by vibrations as well as chemical means and typically provide food rewards. | Caterpillar | Wikipedia | 407 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Some caterpillars are gregarious; large aggregations are believed to help in reducing the levels of parasitization and predation. Clusters amplify the signal of aposematic coloration, and individuals may participate in group regurgitation or displays. Pine processionary (Thaumetopoea pityocampa) caterpillars often link into a long train to move through trees and over the ground. The head of the lead caterpillar is visible, but the other heads can appear hidden. Forest tent caterpillars cluster during periods of cold weather.
Predators
Caterpillars are eaten by many animals. The European pied flycatcher is one species that preys upon caterpillars. The flycatcher typically finds caterpillars among oak foliage. Paper wasps, including those in the genus Polistes and Polybia catch caterpillars to feed their young and themselves.
Behavior
Caterpillars have been called "eating machines", and eat leaves voraciously. Most species shed their skin four or five times as their bodies grow, and they eventually enter a pupal stage before becoming adults. Caterpillars grow very quickly; for instance, a tobacco hornworm will increase its weight ten-thousandfold in less than twenty days. An adaptation that enables them to eat so much is a mechanism in a specialized midgut that quickly transports ions to the lumen (midgut cavity), to keep the potassium level higher in the midgut cavity than in the hemolymph.
Most caterpillars are solely herbivorous. Many are restricted to feeding on one species of plant, while others are polyphagous. Some, including the clothes moth, feed on detritus. Some are predatory, and may prey on other species of caterpillars (e.g. Hawaiian Eupithecia). Others feed on eggs of other insects, aphids, scale insects, or ant larvae. A few are parasitic on cicadas or leaf hoppers (Epipyropidae). Some Hawaiian caterpillars (Hyposmocoma molluscivora) use silk traps to capture snails. | Caterpillar | Wikipedia | 448 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Many caterpillars are nocturnal. For example, the "cutworms" (of the family Noctuidae) hide at the base of plants during the day and only feed at night. Others, such as spongy moth (Lymantria dispar) larvae, change their activity patterns depending on density and larval stage, with more diurnal feeding in early instars and high densities.
Economic effects
Caterpillars cause much damage, mainly by eating leaves. The propensity for damage is enhanced by monocultural farming practices, especially where the caterpillar is specifically adapted to the host plant under cultivation. The cotton bollworm causes enormous losses. Other species eat food crops. Caterpillars have been the target of pest control through the use of pesticides, biological control and agronomic practices. Many species have become resistant to pesticides. Bacterial toxins such as those from Bacillus thuringiensis which are evolved to affect the gut of Lepidoptera have been used in sprays of bacterial spores, toxin extracts and also by incorporating genes to produce them within the host plants. These approaches are defeated over time by the evolution of resistance mechanisms in the insects.
Plants evolve mechanisms of resistance to being eaten by caterpillars, including the evolution of chemical toxins and physical barriers such as hairs. Incorporating host plant resistance (HPR) through plant breeding is another approach used in reducing the impact of caterpillars on crop plants.
Some caterpillars are used in industry. The silk industry is based on the silkworm caterpillar.
Human health
Caterpillar hair can be a cause of human health problems. Caterpillar hairs sometimes have venoms in them and species from approximately 12 families of moths or butterflies worldwide can inflict serious human injuries ranging from urticarial dermatitis and atopic asthma to osteochondritis, consumption coagulopathy, kidney failure, and brain bleeding. Skin rashes are the most common, but there have been fatalities. Lonomia is a frequent cause of envenomation in Brazil, with 354 cases reported between 1989 and 2005. Lethality ranging up to 20% with death caused most often by intracranial hemorrhage. | Caterpillar | Wikipedia | 456 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Caterpillar hair has also been known to cause kerato-conjunctivitis. The sharp barbs on the end of caterpillar hairs can get lodged in soft tissues and mucous membranes such as the eyes. Once they enter such tissues, they can be difficult to extract, often exacerbating the problem as they migrate across the membrane.
This becomes a particular problem in an indoor setting. The hair easily enter buildings through ventilation systems and accumulate in indoor environments because of their small size, which makes it difficult for them to be vented out. This accumulation increases the risk of human contact in indoor environments.
Caterpillars are a food source in some cultures. For example, in South Africa mopane worms are eaten by the bushmen, and in China silkworms are considered a delicacy.
In popular culture
In the Old Testament of the Bible caterpillars are feared as pests that devour crops. They are part of the "pestilence, blasting, mildew, locust" because of their association with the locust, thus they are one of the plagues of Egypt. Jeremiah names them as one of the inhabitants of Babylon. The English word caterpillar derives from the old French catepelose (hairy cat) but merged with the piller (pillager). Caterpillars became a symbol for social dependents. Shakespeare's Bolingbroke described King Richard's friends as "The caterpillars of the commonwealth, Which I have sworn to weed and pluck away". In 1790 William Blake referenced this popular image in The Marriage of Heaven and Hell when he attacked priests: "as the caterpillar chooses the fairest leaves to lay her eggs on, so the priest lay his curse on the fairest joys". | Caterpillar | Wikipedia | 371 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
The role of caterpillars in the life stages of butterflies was badly understood. In 1679 Maria Sibylla Merian published the first volume of The Caterpillars' Marvelous Transformation and Strange Floral Food, which contained 50 illustrations and a description of insects, moths, butterflies and their larvae. An earlier popular publication on moths and butterflies, and their caterpillars, by Jan Goedart had not included eggs in the life stages of European moths and butterflies, because he had believed that caterpillars were generated from water. When Merian published her study of caterpillars it was still widely believed that insects were spontaneously generated. Merian's illustrations supported the findings of Francesco Redi, Marcello Malpighi and Jan Swammerdam.
Butterflies were regarded as symbol for the human soul since ancient time, and also in the Christian tradition. Goedart thus located his empirical observations on the transformation of caterpillars into butterflies in the Christian tradition. As such he argued that the metamorphosis from caterpillar into butterfly was a symbol, and even proof, of Christ's resurrection. He argued "that from dead caterpillars emerge living animals; so it is equally true and miraculous, that our dead and rotten corpses will rise from the grave." Swammerdam, who in 1669 had demonstrated that inside a caterpillar the rudiments of the future butterfly's limbs and wings could be discerned, attacked the mystical and religious notion that the caterpillar died and the butterfly subsequently resurrected. As a militant Cartesian, Swammerdam attacked Goedart as ridiculous, and when publishing his findings he proclaimed "here we witness the digression of those who have tried to prove Resurrection of the Dead from these obviously natural and comprehensible changes within the creature itself."
Since then the metamorphoses of the caterpillar into a butterfly has in Western societies been associated with countless human transformations in folktales and literature. There is no process in the physical life of human beings that resembles this metamorphoses, and the symbol of the caterpillar tends to depict a psychic transformation of a human. As such the caterpillar has in the Christian tradition become a metaphor for being "born again". | Caterpillar | Wikipedia | 466 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Famously, in Lewis Carroll's Alice's Adventures in Wonderland a caterpillar asks Alice "Who are you?". When Alice comments on the caterpillar's inevitable transformation into a butterfly, the caterpillar champions the position that in spite of changes it is still possible to know something, and that Alice is the same Alice at the beginning and end of a considerable interval. When the Caterpillar asks Alice to clarify a point, the child replies "I'm afraid I can't put it more clearly... for I can't but understand it myself, to begin with, and being so many different sizes in a day is very confusing". Here Carroll satirizes René Descartes, the founder of Cartesian philosophy, and his theory on innate ideas. Descartes argued that we are distracted by urgent bodily stimuli that swamp the human mind in childhood. Descartes also theorised that inherited preconceived opinions obstruct the human perception of the truth.
More recent symbolic references to caterpillars in popular media include the Mad Men season 3 episode "The Fog", in which Betty Draper has a drug-induced dream, while in labor, that she captures a caterpillar and holds it firmly in her hand. In The Sopranos season 5 episode "The Test Dream", Tony Soprano dreams that Ralph Cifaretto has a caterpillar on his bald head that changes into a butterfly.
Gallery
Click left or right for a slide show. | Caterpillar | Wikipedia | 308 | 48337 | https://en.wikipedia.org/wiki/Caterpillar | Biology and health sciences | Lepidoptera | Animals |
Butterflies are winged insects from the lepidopteran suborder Rhopalocera, characterized by large, often brightly coloured wings that often fold together when at rest, and a conspicuous, fluttering flight. The group comprises the superfamilies Hedyloidea (moth-butterflies in the Americas) and Papilionoidea (all others). The oldest butterfly fossils have been dated to the Paleocene, about 56 million years ago, though molecular evidence suggests that they likely originated in the Cretaceous.
Butterflies have a four-stage life cycle, and like other holometabolous insects they undergo complete metamorphosis. Winged adults lay eggs on the food plant on which their larvae, known as caterpillars, will feed. The caterpillars grow, sometimes very rapidly, and when fully developed, pupate in a chrysalis. When metamorphosis is complete, the pupal skin splits, the adult insect climbs out, expands its wings to dry, and flies off.
Some butterflies, especially in the tropics, have several generations in a year, while others have a single generation, and a few in cold locations may take several years to pass through their entire life cycle.
Butterflies are often polymorphic, and many species make use of camouflage, mimicry, and aposematism to evade their predators. Some, like the monarch and the painted lady, migrate over long distances. Many butterflies are attacked by parasites or parasitoids, including wasps, protozoans, flies, and other invertebrates, or are preyed upon by other organisms. Some species are pests because in their larval stages they can damage domestic crops or trees; other species are agents of pollination of some plants. Larvae of a few butterflies (e.g., harvesters) eat harmful insects, and a few are predators of ants, while others live as mutualists in association with ants. Culturally, butterflies are a popular motif in the visual and literary arts. The Smithsonian Institution says "butterflies are certainly one of the most appealing creatures in nature".
Etymology | Butterfly | Wikipedia | 422 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
The Oxford English Dictionary derives the word straightforwardly from Old English butorflēoge, butter-fly; similar names in Old Dutch and Old High German show that the name is ancient, but modern Dutch and German use different words ( and ) and the common name often varies substantially between otherwise closely related languages. A possible source of the name is the bright yellow male of the brimstone (Gonepteryx rhamni); another is that butterflies were on the wing in meadows during the spring and summer butter season while the grass was growing.
Paleontology
The earliest Lepidoptera fossils date to the Triassic-Jurassic boundary, around 200million years ago. Butterflies evolved from moths, so while the butterflies are monophyletic (forming a single clade), the moths are not. The oldest known butterfly is Protocoeliades kristenseni from the Palaeocene aged Fur Formation of Denmark, approximately 55million years old, which belongs to the family Hesperiidae (skippers). Molecular clock estimates suggest that butterflies originated sometime in the Late Cretaceous, but only significantly diversified during the Cenozoic, with one study suggesting a North American origin for the group. The oldest American butterfly is the Late Eocene Prodryas persephone from the Florissant Fossil Beds, approximately 34million years old.
Taxonomy and phylogeny
Butterflies are divided into seven families that contain a total of about 20,000 species.
Traditionally, butterflies have been divided into the superfamilies Papilionoidea and the moth-like Hedyloidea. Recent work has discovered that Hedylidae, the only family within Hedyloidea, is nested within the Papilionoidea, meaning that Papilionoidea would be synonymous with Rhopalocera. The relationships between the rest of the 6 families are extremely well resolved, which is summarized in the below cladogram.
Biology
General description
Butterfly adults are characterized by their four scale-covered wings, which give the Lepidoptera their name (Ancient Greek λεπίς lepís, scale + πτερόν pterón, wing). These scales give butterfly wings their colour: they are pigmented with melanins that give them blacks and browns, as well as uric acid derivatives and flavones that give them yellows, but many of the blues, greens, reds and iridescent colours are created by structural coloration produced by the micro-structures of the scales and hairs. | Butterfly | Wikipedia | 507 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
As in all insects, the body is divided into three sections: the head, thorax, and abdomen. The thorax is composed of three segments, each with a pair of legs. In most families of butterfly the antennae are clubbed, unlike those of moths which may be threadlike or feathery. The long proboscis can be coiled when not in use for sipping nectar from flowers.
Nearly all butterflies are diurnal, have relatively bright colours, and hold their wings vertically above their bodies when at rest, unlike the majority of moths which fly by night, are often cryptically coloured (well camouflaged), and either hold their wings flat (touching the surface on which the moth is standing) or fold them closely over their bodies. Some day-flying moths, such as the hummingbird hawk-moth, are exceptions to these rules.
Butterfly larvae, caterpillars, have a hard (sclerotised) head with strong mandibles used for cutting their food, most often leaves. They have cylindrical bodies, with ten segments to the abdomen, generally with short prolegs on segments 3–6 and 10; the three pairs of true legs on the thorax have five segments each. Many are well camouflaged; others are aposematic with bright colours and bristly projections containing toxic chemicals obtained from their food plants. The pupa or chrysalis, unlike that of moths, is not wrapped in a cocoon.
Many butterflies are sexually dimorphic. Most butterflies have the ZW sex-determination system where females are the heterogametic sex (ZW) and males homogametic (ZZ).
Distribution and migration
Butterflies are distributed worldwide except Antarctica, totalling some 18,500 species. Of these, 775 are Nearctic; 7,700 Neotropical; 1,575 Palearctic; 3,650 Afrotropical; and 4,800 are distributed across the combined Oriental and Australian/Oceania regions. The monarch butterfly is native to the Americas, but in the nineteenth century or before, spread across the world, and is now found in Australia, New Zealand, other parts of Oceania, and the Iberian Peninsula. It is not clear how it dispersed; adults may have been blown by the wind or larvae or pupae may have been accidentally transported by humans, but the presence of suitable host plants in their new environment was a necessity for their successful establishment. | Butterfly | Wikipedia | 489 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Many butterflies, such as the painted lady, monarch, and several danaine migrate for long distances. These migrations take place over a number of generations and no single individual completes the whole trip. The eastern North American population of monarchs can travel thousands of miles south-west to overwintering sites in Mexico. There is a reverse migration in the spring. It has recently been shown that the British painted lady undertakes a 9,000-mile round trip in a series of steps by up to six successive generations, from tropical Africa to the Arctic Circle — almost double the length of the famous migrations undertaken by monarch. Spectacular large-scale migrations associated with the monsoon are seen in peninsular India. Migrations have been studied in more recent times using wing tags and also using stable hydrogen isotopes.
Butterflies navigate using a time-compensated sun compass. They can see polarized light and therefore orient even in cloudy conditions. The polarized light near the ultraviolet spectrum appears to be particularly important. Many migratory butterflies live in semi-arid areas where breeding seasons are short. The life histories of their host plants also influence butterfly behaviour.
Life cycle
Butterflies in their adult stage can live from a week to nearly a year depending on the species. Many species have long larval life stages while others can remain dormant in their pupal or egg stages and thereby survive winters. The Melissa Arctic (Oeneis melissa) overwinters twice as a caterpillar. Butterflies may have one or more broods per year. The number of generations per year varies from temperate to tropical regions with tropical regions showing a trend towards multivoltinism.
Courtship is often aerial and often involves pheromones. Butterflies then land on the ground or on a perch to mate. Copulation takes place tail-to-tail and may last from minutes to hours. Simple photoreceptor cells located at the genitals are important for this and other adult behaviours. The male passes a spermatophore to the female; to reduce sperm competition, he may cover her with his scent, or in some species such as the Apollos (Parnassius) plugs her genital opening to prevent her from mating again. | Butterfly | Wikipedia | 443 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
The vast majority of butterflies have a four-stage life cycle: egg, larva (caterpillar), pupa (chrysalis) and imago (adult). In the genera Colias, Erebia, Euchloe, and Parnassius, a small number of species are known that reproduce semi-parthenogenetically; when the female dies, a partially developed larva emerges from her abdomen.
Eggs
Butterfly eggs are protected by a hard-ridged outer layer of shell, called the chorion. This is lined with a thin coating of wax which prevents the egg from drying out before the larva has had time to fully develop. Each egg contains a number of tiny funnel-shaped openings at one end, called micropyles; the purpose of these holes is to allow sperm to enter and fertilize the egg. Butterfly eggs vary greatly in size and shape between species, but are usually upright and finely sculptured. Some species lay eggs singly, others in batches. Many females produce between one hundred and two hundred eggs.
Butterfly eggs are fixed to a leaf with a special glue which hardens rapidly. As it hardens it contracts, deforming the shape of the egg. This glue is easily seen surrounding the base of every egg forming a meniscus. The nature of the glue has been little researched but in the case of Pieris brassicae, it begins as a pale yellow granular secretion containing acidophilic proteins. This is viscous and darkens when exposed to air, becoming a water-insoluble, rubbery material which soon sets solid. Butterflies in the genus Agathymus do not fix their eggs to a leaf; instead, the newly laid eggs fall to the base of the plant.
Eggs are almost invariably laid on plants. Each species of butterfly has its own host plant range and while some species of butterfly are restricted to just one species of plant, others use a range of plant species, often including members of a common family. In some species, such as the great spangled fritillary, the eggs are deposited close to but not on the food plant. This most likely happens when the egg overwinters before hatching and where the host plant loses its leaves in winter, as do violets in this example. | Butterfly | Wikipedia | 471 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
The egg stage lasts a few weeks in most butterflies, but eggs laid close to winter, especially in temperate regions, go through a diapause (resting) stage, and the hatching may take place only in spring. Some temperate region butterflies, such as the Camberwell beauty, lay their eggs in the spring and have them hatch in the summer.
Caterpillar larva
Butterfly larvae, or caterpillars, consume plant leaves and spend practically all of their time searching for and eating food. Although most caterpillars are herbivorous, a few species are predators: Spalgis epius eats scale insects, while lycaenids such as Liphyra brassolis are myrmecophilous, eating ant larvae.
Some larvae, especially those of the Lycaenidae, form mutual associations with ants. They communicate with the ants using vibrations that are transmitted through the substrate as well as using chemical signals. The ants provide some degree of protection to these larvae and they in turn gather honeydew secretions. Large blue (Phengaris arion) caterpillars trick Myrmica ants into taking them back to the ant colony where they feed on the ant eggs and larvae in a parasitic relationship.
Caterpillars mature through a series of developmental stages known as instars. Near the end of each stage, the larva undergoes a process called apolysis, mediated by the release of a series of neurohormones. During this phase, the cuticle, a tough outer layer made of a mixture of chitin and specialized proteins, is released from the softer epidermis beneath, and the epidermis begins to form a new cuticle. At the end of each instar, the larva moults, the old cuticle splits and the new cuticle expands, rapidly hardening and developing pigment. | Butterfly | Wikipedia | 382 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Caterpillars have short antennae and several simple eyes. The mouthparts are adapted for chewing with powerful mandibles and a pair of maxillae, each with a segmented palp. Adjoining these is the labium-hypopharynx which houses a tubular spinneret which is able to extrude silk. Caterpillars such as those in the genus Calpodes (family Hesperiidae) have a specialized tracheal system on the 8th segment that function as a primitive lung. Butterfly caterpillars have three pairs of true legs on the thoracic segments and up to six pairs of prolegs arising from the abdominal segments. These prolegs have rings of tiny hooks called crochets that are engaged hydrostatically and help the caterpillar grip the substrate. The epidermis bears tufts of setae, the position and number of which help in identifying the species. There is also decoration in the form of hairs, wart-like protuberances, horn-like protuberances and spines. Internally, most of the body cavity is taken up by the gut, but there may also be large silk glands, and special glands which secrete distasteful or toxic substances. The developing wings are present in later stage instars and the gonads start development in the egg stage.
Pupa | Butterfly | Wikipedia | 280 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
When the larva is fully grown, hormones such as prothoracicotropic hormone (PTTH) are produced. At this point the larva stops feeding, and begins "wandering" in the quest for a suitable pupation site, often the underside of a leaf or other concealed location. There it spins a button of silk which it uses to fasten its body to the surface and moults for a final time. While some caterpillars spin a cocoon to protect the pupa, most species do not. The naked pupa, often known as a chrysalis, usually hangs head down from the cremaster, a spiny pad at the posterior end, but in some species a silken girdle may be spun to keep the pupa in a head-up position. Most of the tissues and cells of the larva are broken down inside the pupa, as the constituent material is rebuilt into the imago. The structure of the transforming insect is visible from the exterior, with the wings folded flat on the ventral surface and the two halves of the proboscis, with the antennae and the legs between them.
The pupal transformation into a butterfly through metamorphosis has held great appeal to mankind. To transform from the miniature wings visible on the outside of the pupa into large structures usable for flight, the pupal wings undergo rapid mitosis and absorb a great deal of nutrients. If one wing is surgically removed early on, the other three will grow to a larger size. In the pupa, the wing forms a structure that becomes compressed from top to bottom and pleated from proximal to distal ends as it grows, so that it can rapidly be unfolded to its full adult size. Several boundaries seen in the adult colour pattern are marked by changes in the expression of particular transcription factors in the early pupa.
Adult | Butterfly | Wikipedia | 380 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
The reproductive stage of the insect is the winged adult or imago. The surface of both butterflies and moths is covered by scales, each of which is an outgrowth from a single epidermal cell. The head is small and dominated by the two large compound eyes. These are capable of distinguishing flower shapes or motion but cannot view distant objects clearly. Colour perception is good, especially in some species in the blue/violet range. The antennae are composed of many segments and have clubbed tips (unlike moths that have tapering or feathery antennae). The sensory receptors are concentrated in the tips and can detect odours. Taste receptors are located on the palps and on the feet. The mouthparts are adapted to sucking and the mandibles are usually reduced in size or absent. The first maxillae are elongated into a tubular proboscis which is curled up at rest and expanded when needed to feed. The first and second maxillae bear palps which function as sensory organs. Some species have a reduced proboscis or maxillary palps and do not feed as adults.
Many Heliconius butterflies also use their proboscis to feed on pollen; in these species only 20% of the amino acids used in reproduction come from larval feeding, which allow them to develop more quickly as caterpillars, and gives them a longer lifespan of several months as adults.
The thorax of the butterfly is devoted to locomotion. Each of the three thoracic segments has two legs (among nymphalids, the first pair is reduced and the insects walk on four legs). The second and third segments of the thorax bear the wings. The leading edges of the forewings have thick veins to strengthen them, and the hindwings are smaller and more rounded and have fewer stiffening veins. The forewings and hindwings are not hooked together (as they are in moths) but are coordinated by the friction of their overlapping parts. The front two segments have a pair of spiracles which are used in respiration. | Butterfly | Wikipedia | 412 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
The abdomen consists of ten segments and contains the gut and genital organs. The front eight segments have spiracles and the terminal segment is modified for reproduction. The male has a pair of clasping organs attached to a ring structure, and during copulation, a tubular structure is extruded and inserted into the female's vagina. A spermatophore is deposited in the female, following which the sperm make their way to a seminal receptacle where they are stored for later use. In both sexes, the genitalia are adorned with various spines, teeth, scales and bristles, which act to prevent the butterfly from mating with an insect of another species. After it emerges from its pupal stage, a butterfly cannot fly until the wings are unfolded. A newly emerged butterfly needs to spend some time inflating its wings with hemolymph and letting them dry, during which time it is extremely vulnerable to predators.
Pattern formation
The colourful patterns on many butterfly wings tell potential predators that they are toxic. Hence, the genetic basis of wing pattern formation can illuminate both the evolution of butterflies as well as their developmental biology. The colour of butterfly wings is derived from tiny structures called scales, each of which have their own pigments. In Heliconius butterflies, there are three types of scales: yellow/white, black, and red/orange/brown scales. Some mechanism of wing pattern formation are now being solved using genetic techniques. For instance, a gene called cortex determines the colour of scales: deleting cortex turned black and red scales yellow. Mutations, e.g. transposon insertions of the non-coding DNA around the cortex gene can turn a black-winged butterfly into a butterfly with a yellow wing band. | Butterfly | Wikipedia | 357 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Mating
When the butterfly Bicyclus anynana is subjected to repeated inbreeding in the laboratory, there is a dramatic decrease in egg hatching. This severe inbreeding depression is considered to be likely due to a relatively high mutation rate to recessive alleles with substantial damaging effects and infrequent episodes of inbreeding in nature that might otherwise purge such mutations. Although B. anynana experiences inbreeding depression when forcibly inbred in the laboratory it recovers within a few generation when allowed to breed freely. During mate selection, adult females do not innately avoid or learn to avoid siblings, implying that such detection may not be critical to reproductive fitness. Inbreeding may persist in B anynana because the probability of encountering close relatives is rare in nature; that is, movement ecology may mask the deleterious effect of inbreeding resulting in relaxation of selection for active inbreeding avoidance behaviors.
Behaviour
Butterflies feed primarily on nectar from flowers. Some also derive nourishment from pollen, tree sap, rotting fruit, dung, decaying flesh, and dissolved minerals in wet sand or dirt. Butterflies are important as pollinators for some species of plants. In general, they do not carry as much pollen load as bees, but they are capable of moving pollen over greater distances. Flower constancy has been observed for at least one species of butterfly.
Adult butterflies consume only liquids, ingested through the proboscis. They sip water from damp patches for hydration and feed on nectar from flowers, from which they obtain sugars for energy, and sodium and other minerals vital for reproduction. Several species of butterflies need more sodium than that provided by nectar and are attracted by sodium in salt; they sometimes land on people, attracted by the salt in human sweat. Some butterflies also visit dung and scavenge rotting fruit or carcasses to obtain minerals and nutrients. In many species, this mud-puddling behaviour is restricted to the males, and studies have suggested that the nutrients collected may be provided as a nuptial gift, along with the spermatophore, during mating.
In hilltopping, males of some species seek hilltops and ridge tops, which they patrol in search for females. Since it usually occurs in species with low population density, it is assumed these landscape points are used as meeting places to find mates. | Butterfly | Wikipedia | 481 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Butterflies use their antennae to sense the air for wind and scents. The antennae come in various shapes and colours; the hesperiids have a pointed angle or hook to the antennae, while most other families show knobbed antennae. The antennae are richly covered with sensory organs known as sensillae. A butterfly's sense of taste is coordinated by chemoreceptors on the tarsi, or feet, which work only on contact, and are used to determine whether an egg-laying insect's offspring will be able to feed on a leaf before eggs are laid on it. Many butterflies use chemical signals, pheromones; some have specialized scent scales (androconia) or other structures (coremata or "hair pencils" in the Danaidae). Vision is well developed in butterflies and most species are sensitive to the ultraviolet spectrum. Many species show sexual dimorphism in the patterns of UV reflective patches. Colour vision may be widespread but has been demonstrated in only a few species. Some butterflies have organs of hearing and some species make stridulatory and clicking sounds.
Many species of butterfly maintain territories and actively chase other species or individuals that may stray into them. Some species will bask or perch on chosen perches. The flight styles of butterflies are often characteristic and some species have courtship flight displays. Butterflies can only fly when their temperature is above ; when it is cool, they can position themselves to expose the underside of the wings to the sunlight to heat themselves up. If their body temperature reaches , they can orientate themselves with the folded wings edgewise to the sun. Basking is an activity which is more common in the cooler hours of the morning. Some species have evolved dark wingbases to help in gathering more heat and this is especially evident in alpine forms.
As in many other insects, the lift generated by butterflies is more than can be accounted for by steady-state, non-transitory aerodynamics. Studies using Vanessa atalanta in a wind tunnel show that they use a wide variety of aerodynamic mechanisms to generate force. These include wake capture, vortices at the wing edge, rotational mechanisms and the Weis-Fogh 'clap-and-fling' mechanism. Butterflies are able to change from one mode to another rapidly.
Ecology
Parasitoids, predators, and pathogens | Butterfly | Wikipedia | 473 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Butterflies are threatened in their early stages by parasitoids and in all stages by predators, diseases and environmental factors. Braconid and other parasitic wasps lay their eggs in lepidopteran eggs or larvae and the wasps' parasitoid larvae devour their hosts, usually pupating inside or outside the desiccated husk. Most wasps are very specific about their host species and some have been used as biological controls of pest butterflies like the large white butterfly. When the small cabbage white was accidentally introduced to New Zealand, it had no natural enemies. In order to control it, some pupae that had been parasitised by a chalcid wasp were imported, and natural control was thus regained. Some flies lay their eggs on the outside of caterpillars and the newly hatched fly larvae bore their way through the skin and feed in a similar way to the parasitoid wasp larvae. Predators of butterflies include ants, spiders, wasps, and birds.
Caterpillars are also affected by a range of bacterial, viral and fungal diseases, and only a small percentage of the butterfly eggs laid ever reach adulthood. The bacterium Bacillus thuringiensis has been used in sprays to reduce damage to crops by the caterpillars of the large white butterfly, and the entomopathogenic fungus Beauveria bassiana has proved effective for the same purpose.
Endangered species
Queen Alexandra's birdwing, found in Papua New Guinea, is the largest butterfly in the world. The species is endangered, and is one of only three insects (the other two being butterflies as well) to be listed on Appendix I of CITES, making international trade illegal.
Defences
Butterflies protect themselves from predators by a variety of means. | Butterfly | Wikipedia | 349 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Chemical defences are widespread and are mostly based on chemicals of plant origin. In many cases the plants themselves evolved these toxic substances as protection against herbivores. Butterflies have evolved mechanisms to sequester these plant toxins and use them instead in their own defence. These defence mechanisms are effective only if they are well advertised; this has led to the evolution of bright colours in unpalatable butterflies (aposematism). This signal is commonly mimicked by other butterflies, usually only females. A Batesian mimic imitates another species to enjoy the protection of that species' aposematism. The common Mormon of India has female morphs which imitate the unpalatable red-bodied swallowtails, the common rose and the crimson rose. Müllerian mimicry occurs when aposematic species evolve to resemble each other, presumably to reduce predator sampling rates; Heliconius butterflies from the Americas are a good example.
Camouflage is found in many butterflies. Some like the oakleaf butterfly and autumn leaf are remarkable imitations of leaves. As caterpillars, many defend themselves by freezing and appearing like sticks or branches. Others have deimatic behaviours, such as rearing up and waving their front ends which are marked with eyespots as if they were snakes. Some papilionid caterpillars such as the giant swallowtail (Papilio cresphontes) resemble bird droppings so as to be passed over by predators. Some caterpillars have hairs and bristly structures that provide protection while others are gregarious and form dense aggregations. Some species are myrmecophiles, forming mutualistic associations with ants and gaining their protection. Behavioural defences include perching and angling the wings to reduce shadow and avoid being conspicuous. Some female Nymphalid butterflies guard their eggs from parasitoidal wasps.
The Lycaenidae have a false head consisting of eyespots and small tails (false antennae) to deflect attack from the more vital head region. These may also cause ambush predators such as spiders to approach from the wrong end, enabling the butterflies to detect attacks promptly. Many butterflies have eyespots on the wings; these too may deflect attacks, or may serve to attract mates.
Auditory defences can also be used, which in the case of the grizzled skipper refers to vibrations generated by the butterfly upon expanding its wings in an attempt to communicate with ant predators. | Butterfly | Wikipedia | 500 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Many tropical butterflies have seasonal forms for dry and wet seasons. These are switched by the hormone ecdysone. The dry-season forms are usually more cryptic, perhaps offering better camouflage when vegetation is scarce. Dark colours in wet-season forms may help to absorb solar radiation.
Butterflies without defences such as toxins or mimicry protect themselves through a flight that is more bumpy and unpredictable than in other species. It is assumed this behavior makes it more difficult for predators to catch them, and is caused by the turbulence created by the small whirlpools formed by the wings during flight.
Declining numbers
Declining butterfly populations have been noticed in many areas of the world, and this phenomenon is consistent with the rapidly decreasing insect populations around the world. At least in the Western United States, this collapse in the number of most species of butterflies has been determined to be driven by global climate change, specifically, by warmer autumns.
In culture
In art and literature
Butterflies have appeared in art from 3500 years ago in ancient Egypt. In hunting scenes, butterflies were sometimes included in a way that suggested life, freedom, and the strength to escape capture, creating a balance to scenes concerned with death and upholding ma'at. They also were suggestive of regeneration or rebirth and protection. Certain butterflies, such as the tiger butterfly, may have been associated with solar deities, particularly Ra. The tiger butterfly also would have a particular resemblance to the ankh, due to its black body and wingtips, that was likely noted by the Ancient Egyptians. Butterflies may also have been understood as one of the deceased's guides in the afterlife.
In the ancient Mesoamerican city of Teotihuacan, the brilliantly coloured image of the butterfly was carved into many temples, buildings, jewellery, and emblazoned on incense burners. The butterfly was sometimes depicted with the maw of a jaguar, and some species were considered to be the reincarnations of the souls of dead warriors. The close association of butterflies with fire and warfare persisted into the Aztec civilisation; evidence of similar jaguar-butterfly images has been found among the Zapotec and Maya civilisations.
Butterflies are widely used in objects of art and jewellery: mounted in frames, embedded in resin, displayed in bottles, laminated in paper, and used in some mixed media artworks and furnishings. The Norwegian naturalist Kjell Sandved compiled a photographic Butterfly Alphabet containing all 26 letters and the numerals 0 to 9 from the wings of butterflies. | Butterfly | Wikipedia | 510 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Sir John Tenniel drew a famous illustration of Alice meeting a caterpillar for Lewis Carroll's Alice in Wonderland, c. 1865. The caterpillar is seated on a toadstool and is smoking a hookah; the image can be read as showing either the forelegs of the larva, or as suggesting a face with protruding nose and chin. Eric Carle's children's book The Very Hungry Caterpillar portrays the larva as an extraordinarily hungry animal, while also teaching children how to count (to five) and the days of the week.
A butterfly appeared in one of Rudyard Kipling's Just So Stories, "The Butterfly that Stamped".
One of the most popular, and most often recorded, songs by Sweden's eighteenth-century bard, Carl Michael Bellman, is "Fjäriln vingad syns på Haga" (The butterfly wingèd is seen in Haga), one of his Fredman's Songs.
Madam Butterfly is a 1904 opera by Giacomo Puccini about a romantic young Japanese bride who is deserted by her American officer husband soon after they are married. It was based on John Luther Long's short story written in 1898.
In mythology and folklore
According to Lafcadio Hearn, a butterfly was seen in Japan as the personification of a person's soul; whether they be living, dying, or already dead. One Japanese superstition says that if a butterfly enters your guest room and perches behind the bamboo screen, the person whom you most love is coming to see you. Large numbers of butterflies are viewed as bad omens. When Taira no Masakado was secretly preparing his famous revolt, a vast a swarm of butterflies appeared in Kyoto. The people were frightened, thinking the apparition to be a portent of coming evil. | Butterfly | Wikipedia | 380 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
Diderot's Encyclopédie cites butterflies as a symbol for the soul. A Roman sculpture depicts a butterfly exiting the mouth of a dead man, representing the Roman belief that the soul leaves through the mouth. In line with this, the ancient Greek word for "butterfly" is ψυχή (psȳchē), which primarily means "soul" or "mind". According to Mircea Eliade, some of the Nagas of Manipur claim ancestry from a butterfly. In some cultures, butterflies symbolise rebirth. The butterfly is a symbol of being transgender, because of the transformation from caterpillar to winged adult. In the English county of Devon, people once hurried to kill the first butterfly of the year, to avoid a year of bad luck. In the Philippines, a lingering black or dark butterfly or moth in the house is taken to mean an impending or recent death in the family. Several American states have chosen an official state butterfly.
Collecting, recording, and rearing
"Collecting" means preserving dead specimens, not keeping butterflies as pets. Collecting butterflies was once a popular hobby; it has now largely been replaced by photography, recording, and rearing butterflies for release into the wild. The zoological illustrator Frederick William Frohawk succeeded in rearing all the butterfly species found in Britain, at a rate of four per year, to enable him to draw every stage of each species. He published the results in the folio sized handbook The Natural History of British Butterflies in 1924.
Butterflies and moths can be reared for recreation or for release.
In technology
Study of the structural coloration of the wing scales of swallowtail butterflies has led to the development of more efficient light-emitting diodes, and is inspiring nanotechnology research to produce paints that do not use toxic pigments and the development of new display technologies. | Butterfly | Wikipedia | 370 | 48338 | https://en.wikipedia.org/wiki/Butterfly | Biology and health sciences | Lepidoptera | null |
A parachute is a device used to slow the motion of an object through an atmosphere by creating drag or aerodynamic lift. A major application is to support people, for recreation or as a safety device for aviators, who can exit from an aircraft at height and descend safely to earth.
A parachute is usually made of a light, strong fabric. Early parachutes were made of silk. The most common fabric today is nylon. A parachute's canopy is typically dome-shaped, but some are rectangles, inverted domes, and other shapes.
A variety of loads are attached to parachutes, including people, food, equipment, space capsules, and bombs.
History
Middle Ages
In 852, in Córdoba, Spain, the Moorish man Armen Firman attempted unsuccessfully to fly by jumping from a tower while wearing a large cloak. It was recorded that "there was enough air in the folds of his cloak to prevent great injury when he reached the ground."
Early Renaissance
The earliest evidence for the true parachute dates back to the Renaissance period. The oldest parachute design appears in a manuscript from the 1470s attributed to Francesco di Giorgio Martini (British Library, Add MS 34113, fol. 200v), showing a free-hanging man clutching a crossbar frame attached to a conical canopy. As a safety measure, four straps ran from the ends of the rods to a waist belt. Although the surface area of the parachute design appears to be too small to offer effective air resistance and the wooden base-frame is superfluous and potentially harmful, the basic concept of a working parachute is apparent.
The design is a marked improvement over another folio (189v), which depicts a man trying to break the force of his fall using two long cloth streamers fastened to two bars, which he grips with his hands. | Parachute | Wikipedia | 367 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Shortly after, a more sophisticated parachute was sketched by the polymath Leonardo da Vinci in his Codex Atlanticus (fol. 381v) dated to . Here, the scale of the parachute is in a more favorable proportion to the weight of the jumper. A square wooden frame, which alters the shape of the parachute from conical to pyramidal, held open Leonardo's canopy. It is not known whether the Italian inventor was influenced by the earlier design, but he may have learned about the idea through the intensive oral communication among artist-engineers of the time. The feasibility of Leonardo's pyramidal design was successfully tested in 2000 by Briton Adrian Nicholas and again in 2008 by the Swiss skydiver Olivier Vietti-Teppa. According to historian of technology Lynn White, these conical and pyramidal designs, much more elaborate than early artistic jumps with rigid parasols in Asia, mark the origin of "the parachute as we know it."
The Croatian polymath and inventor Fausto Veranzio, or Faust Vrančić (1551–1617), examined da Vinci's parachute sketch and kept the square frame but replaced the canopy with a bulging sail-like piece of cloth that he came to realize decelerates a fall more effectively. A now-famous depiction of a parachute that he dubbed Homo Volans (Flying Man), showing a man parachuting from a tower, presumably St Mark's Campanile in Venice, appeared in his book on mechanics, Machinae Novae ("New Machines", published in 1615 or 1616), alongside a number of other devices and technical concepts.
It was once widely believed that in 1617, Veranzio, then aged 65 and seriously ill, implemented his design and tested the parachute by jumping from St Mark's Campanile, from a bridge nearby, or from St Martin's Cathedral in Bratislava. Various publications incorrectly claimed the event was documented some thirty years later by John Wilkins, one of the founders of, and secretary of, the Royal Society in London, in his book Mathematical Magick or, the Wonders that may be Performed by Mechanical Geometry, published in London in 1648. However, Wilkins wrote about flying, not parachutes, and does not mention Veranzio, a parachute jump, or any event in 1617. Doubts about this test, which include a lack of written evidence, suggest it never occurred, and was instead a misreading of historical notes.
18th and 19th centuries | Parachute | Wikipedia | 507 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
The modern parachute was invented in the late 18th century by Louis-Sébastien Lenormand in France, who made the first recorded public jump in 1783. Lenormand also sketched his device beforehand.
Two years later, in 1785, Lenormand coined the word "parachute" by hybridizing an Italian prefix para, an imperative form of parare = to avert, defend, resist, guard, shield or shroud, from paro = to parry, and chute, the French word for fall, to describe the aeronautical device's real function.
Also in 1785, Jean-Pierre Blanchard demonstrated it as a means of safely disembarking from a hot-air balloon. While Blanchard's first parachute demonstrations were conducted with a dog as the passenger, he later claimed to have had the opportunity to try it himself in 1793 when his hot air balloon ruptured, and he used a parachute to descend. (This event was not witnessed by others.)
On 12 October 1799, Jeanne Geneviève Garnerin ascended in a gondola attached to a balloon. At 900 meters she detached the gondola from the balloon and descended in the gondola by parachute. In doing so, she became the first woman to parachute. She went on to complete many ascents and parachute descents in towns across France and Europe.
Subsequent development of the parachute focused on it becoming more compact. While the early parachutes were made of linen stretched over a wooden frame, in the late 1790s, Blanchard began making parachutes from folded silk, taking advantage of silk's strength and light weight. In 1797, André Garnerin made the first descent of a "frameless" parachute covered in silk. In 1804, Jérôme Lalande introduced a vent in the canopy to eliminate violent oscillations. In 1887, Park Van Tassel and Thomas Scott Baldwin invented a parachute in San Francisco, California, with Baldwin making the first successful parachute jump in the western United States.
Eve of World War I
In 1907 Charles Broadwick demonstrated two key advances in the parachute he used to jump from hot air balloons at fairs: he folded his parachute into a backpack, and the parachute was pulled from the pack by a static line attached to the balloon. When Broadwick jumped from the balloon, the static line became taut, pulled the parachute from the pack, and then snapped. | Parachute | Wikipedia | 480 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
In 1911 a successful test took place with a dummy at the Eiffel Tower in Paris. The puppet's weight was ; the parachute's weight was . The cables between the puppet and the parachute were long. On February 4, 1912, Franz Reichelt jumped to his death from the tower during initial testing of his wearable parachute.
Also in 1911, Grant Morton made the first parachute jump from an airplane, a Wright Model B piloted by Phil Parmalee, at Venice Beach, California. Morton's device was of the "throw-out" type where he held the parachute in his arms as he left the aircraft. In the same year (1911), Russian Gleb Kotelnikov invented the first knapsack parachute, although Hermann Lattemann and his wife Käthe Paulus had been jumping with bagged parachutes in the last decade of the 19th century.
In 1912, on a road near Tsarskoye Selo, years before it became part of St. Petersburg, Kotelnikov successfully demonstrated the braking effects of a parachute by accelerating a Russo-Balt automobile to its top speed and then opening a parachute attached to the back seat, thus also inventing the drogue parachute.
On 1 March 1912, U.S. Army Captain Albert Berry made the first (attached-type) parachute jump in the United States from a fixed-wing aircraft, a Benoist pusher, while flying above Jefferson Barracks, St. Louis, Missouri. The jump utilized a parachute stored or housed in a cone-shaped casing under the airplane and attached to a harness on the jumper's body.
Štefan Banič patented an umbrella-like design in 1914, and sold (or donated) the patent to the United States military, which later modified his design, resulting in the first military parachute. Banič had been the first person to patent the parachute, and his design was the first to properly function in the 20th century.
On June 21, 1913, Georgia Broadwick became the first woman to parachute-jump from a moving aircraft, doing so over Los Angeles, California. In 1914, while doing demonstrations for the U.S. Army, Broadwick deployed her chute manually, thus becoming the first person to jump free-fall.
World War I | Parachute | Wikipedia | 460 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
The first military use of the parachute was by artillery observers on tethered observation balloons in World War I. These were tempting targets for enemy fighter aircraft, though difficult to destroy, due to their heavy anti-aircraft defenses. Because it was difficult to escape from them, and dangerous when on fire due to their hydrogen inflation, observers would abandon them and descend by parachute as soon as enemy aircraft were seen. The ground crew would then attempt to retrieve and deflate the balloon as quickly as possible. The main part of the parachute was in a bag suspended from the balloon with the pilot wearing only a simple waist harness attached to the main parachute. When the balloon crew jumped the main part of the parachute was pulled from the bag by the crew's waist harness, first the shroud lines, followed by the main canopy. This type of parachute was first adopted on a large scale for their observation balloon crews by the Germans, and then later by the British and French. While this type of unit worked well from balloons, it had mixed results when used on fixed-wing aircraft by the Germans, where the bag was stored in a compartment directly behind the pilot. In many instances where it did not work the shroud lines became entangled with the spinning aircraft. Although this type of parachute saved a number of famous German fighter pilots, including Hermann Göring, no parachutes were issued to the crews of Allied "heavier-than-air" aircraft. It has been claimed that the reason was to avoid pilots jumping from the plane when hit rather than trying to save the aircraft, but Air Vice Marshall Arthur Gould Lee, himself a pilot during the war, examined the British War Office files after the war and found no evidence of such claim.
Airplane cockpits at that time also were not large enough to accommodate a pilot and a parachute, since a seat that would fit a pilot wearing a parachute would be too large for a pilot not wearing one. This is why the German type was stowed in the fuselage, rather than being of the "backpack" type. Weight was – at the very beginning – also a consideration since planes had limited load capacity. Carrying a parachute impeded performance and reduced the useful offensive and fuel load. | Parachute | Wikipedia | 443 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
In the UK, Everard Calthrop, a railway engineer and breeder of Arab horses, invented and marketed through his Aerial Patents Company a "British Parachute" and the "Guardian Angel" parachute. As part of an investigation into Calthrop's design, on 13 January 1917, test pilot Clive Franklyn Collett successfully jumped from a Royal Aircraft Factory BE.2c flying over Orford Ness Experimental Station at . He repeated the experiment several days later.
Following on from Collett, balloon officer Thomas Orde-Lees, known as the "Mad Major", successfully jumped from Tower Bridge in London, which led to the balloonists of the Royal Flying Corps using parachutes, though they were issued for use in aircraft.
In 1911, Solomon Lee Van Meter, Jr. of Lexington, Kentucky, submitted an application for, and in July 1916 received, a patent for a backpack style parachute – the Aviatory Life Buoy. His self-contained device featured a revolutionary quick-release mechanism – the ripcord – that allowed a falling aviator to expand the canopy only when safely away from the disabled aircraft.
Otto Heinecke, a German airship ground crewman, designed a parachute which the German air service introduced in 1918, becoming the world's first air service to introduce a standard parachute. Schroeder company of Berlin manufactured Heinecke's design. The first successful use of this parachute was by Leutnant Helmut Steinbrecher of Jagdstaffel 46, who bailed on 27 June 1918 from his stricken fighter airplane to become the first pilot in history to successfully do so. Although many pilots were saved by the Heinecke design, their efficacy was relatively poor. Out of the first 70 German airmen to bail out, around a third died, These fatalities were mostly due to the chute or ripcord becoming entangled in the airframe of their spinning aircraft or because of harness failure, a problem fixed in later versions.
The French, British, American and Italian air services later based their first parachute designs on the Heinecke parachute to varying extents.
In the UK, Sir Frank Mears, who was serving as a Major in the Royal Flying Corps in France (Kite Balloon section), registered a patent in July 1918 for a parachute with a quick release buckle, known as the "Mears parachute", which was in common use from then onwards.
Post-World War I | Parachute | Wikipedia | 490 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
The experience with parachutes during the war highlighted the need to develop a design that could be reliably used to exit a disabled airplane. For instance, tethered parachutes did not work well when the aircraft was spinning. After the war, Major Edward L. Hoffman of the United States Army led an effort to develop an improved parachute by bringing together the best elements of multiple parachute designs. Participants in the effort included Leslie Irvin and James Floyd Smith. The team eventually created the Airplane Parachute Type-A. This incorporated three key elements:
storing the parachute in a soft pack worn on the back, as demonstrated by Charles Broadwick in 1906;
a ripcord for manually deploying the parachute at a safe distance from the airplane, from a design by Albert Leo Stevens; and
a pilot chute that draws the main canopy from the pack.
In 1919, Irvin successfully tested the parachute by jumping from an airplane. The Type-A parachute was put into production and over time saved a number of lives. The effort was recognized by the awarding of the Robert J. Collier Trophy to Major Edward L. Hoffman in 1926.
Irvin became the first person to make a premeditated free-fall parachute jump from an airplane. An early brochure of the Irvin Air Chute Company credits William O'Connor as having become, on 24 August 1920, at McCook Field near Dayton, Ohio, the first person to be saved by an Irvin parachute. Test pilot Lt. Harold R. Harris made another life-saving jump at McCook Field on 20 October 1922. Shortly after Harris' jump, two Dayton newspaper reporters suggested the creation of the Caterpillar Club for successful parachute jumps from disabled aircraft. | Parachute | Wikipedia | 345 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Beginning with Italy in 1927, several countries experimented with using parachutes to drop soldiers behind enemy lines. The regular Soviet Airborne Troops were established as early as 1931 after a number of experimental military mass jumps starting from 2 August 1930. Earlier the same year, the first Soviet mass jumps led to the development of the parachuting sport in the Soviet Union. By the time of World War II, large airborne forces were trained and used in surprise attacks, as in the battles for Fort Eben-Emael and The Hague, the first large-scale, opposed landings of paratroopers in military history, by the Germans. This was followed later in the war by airborne assaults on a larger scale, such as the Battle of Crete and Operation Market Garden, the latter being the largest airborne military operation ever. Aircraft crew were routinely equipped with parachutes for emergencies as well.
In 1937, drag chutes were used in aviation for the first time, by Soviet airplanes in the Arctic that were providing support for the polar expeditions of the era, such as the first drifting ice station, North Pole-1. The drag chute allowed airplanes to land safely on smaller ice floes.
Most parachutes were made of silk until World War II cut off supplies from Japan. After Adeline Gray made the first jump using a nylon parachute in June 1942, the industry switched to nylon.
Types
Today's modern parachutes are classified into two categories – ascending and descending canopies. All ascending canopies refer to paragliders, built specifically to ascend and stay aloft as long as possible. Other parachutes, including ram-air non-elliptical, are classified as descending canopies by manufacturers.
Some modern parachutes are classified as semi-rigid wings, which are maneuverable and can make a controlled descent to collapse on impact with the ground.
Round | Parachute | Wikipedia | 372 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Round parachutes are purely a drag device (that is, unlike the ram-air types, they provide no lift) and are used in military, emergency and cargo applications (e.g. airdrops). Most have large dome-shaped canopies made from a single layer of triangular cloth gores. Some skydivers call them "jellyfish 'chutes" because of the resemblance to the marine organisms. Modern sports parachutists rarely use this type.
The first round parachutes were simple, flat circulars. These early parachutes suffered from instability caused by oscillations. A hole in the apex helped to vent some air and reduce the oscillations. Many military applications adopted conical, i.e., cone-shaped, or parabolic (a flat circular canopy with an extended skirt) shapes, such as the United States Army T-10 static-line parachute. A round parachute with no holes in it is more prone to oscillate and is not considered to be steerable. Some parachutes have inverted dome-shaped canopies. These are primarily used for dropping non-human payloads due to their faster rate of descent.
Forward speed (5–13 km/h) and steering can be achieved by cuts in various sections (gores) across the back, or by cutting four lines in the back, thereby modifying the canopy shape to allow air to escape from the back of the canopy, providing limited forward speed. Other modifications sometimes used are cuts in various gores to cause some of the skirt to bow out. Turning is accomplished by forming the edges of the modifications, giving the parachute more speed from one side of the modification than the other. This gives the jumpers the ability to steer the parachute (such as the United States Army MC series parachutes), enabling them to avoid obstacles and to turn into the wind to minimize horizontal speed at landing.
Cruciform | Parachute | Wikipedia | 391 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
The unique design characteristics of cruciform parachutes decrease oscillation (its user swinging back and forth) and violent turns during descent. This technology will be used by the United States Army as it replaces its older T-10 parachutes with T-11 parachutes under a program called Advanced Tactical Parachute System (ATPS). The ATPS canopy is a highly modified version of a cross/ cruciform platform and is square in appearance. The ATPS system will reduce the rate of descent by 30 percent from to . The T-11 is designed to have an average rate of descent 14% slower than the T-10D, thus resulting in lower landing injury rates for jumpers. The decline in the rate of descent will reduce the impact energy by almost 25% to lessen the potential for injury.
Pull-down apex
A variation on the round parachute is the pull-down apex parachute, invented by a Frenchman named Pierre-Marcel Lemoigne. The first widely used canopy of this type was called the Para-Commander (made by the Pioneer Parachute Co.), although there are many other canopies with a pull-down apex produced in the years thereafter - these had minor differences in attempts to make a higher performance rig, such as different venting configurations. They are all considered 'round' parachutes, but with suspension lines to the canopy apex that apply load there and pull the apex closer to the load, distorting the round shape into a somewhat flattened or lenticular shape when viewed from the side. And while called rounds, they generally have an elliptical shape when viewed from above or below, with the sides bulging out more than the for'd-and-aft dimension, the chord (see the lower photo to the right and you likely can ascertain the difference). | Parachute | Wikipedia | 366 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Due to their lenticular shape and appropriate venting, they have a considerably faster forward speed than, say, a modified military canopy. And due to controllable rear-facing vents in the canopy's sides, they also have much snappier turning capabilities, though they are decidedly low-performance compared to today's ram-air rigs. From about the mid-1960s to the late-1970s, this was the most popular parachute design type for sport parachuting (prior to this period, modified military 'rounds' were generally used and after, ram-air 'squares' became common). Note that the use of the word elliptical for these 'round' parachutes is somewhat dated and may cause slight confusion, since some 'squares' (i.e. ram-airs) are elliptical nowadays, too.
Annular
Some designs with a pull-down apex have the fabric removed from the apex to open a hole through which air can exit (most, if not all, round canopies have at least a small hole to allow easier tie-down for packing - these aren't considered annular), giving the canopy an annular geometry. This hole can be very pronounced in some designs, taking up more 'space' than the parachute. They also have decreased horizontal drag due to their flatter shape and, when combined with rear-facing vents, can have considerable forward speed. Truly annular designs - with a hole large enough that the canopy can be classified as ring-shaped - are uncommon.
Rogallo wing
Sport parachuting has experimented with the Rogallo wing, among other shapes and forms. These were usually an attempt to increase the forward speed and reduce the landing speed offered by the other options at the time. The ram-air parachute's development and the subsequent introduction of the sail slider to slow deployment reduced the level of experimentation in the sport parachuting community. The parachutes are also hard to build.
Ribbon and ring | Parachute | Wikipedia | 401 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Ribbon and ring parachutes have similarities to annular designs. They are frequently designed to deploy at supersonic speeds. A conventional parachute would instantly burst upon opening and be shredded at such speeds. Ribbon parachutes have a ring-shaped canopy, often with a large hole in the centre to release the pressure. Sometimes the ring is broken into ribbons connected by ropes to leak air even more. These large leaks lower the stress on the parachute so it does not burst or shred when it opens. Ribbon parachutes made of Kevlar are used on nuclear bombs, such as the B61 and B83.
Ram-air
The principle of the Ram-Air Multicell Airfoil was conceived in 1963 by Canadian Domina "Dom" C. Jalbert, but serious problems had to be solved before a ram-air canopy could be marketed to the sport parachuting community. Ram-air parafoils are steerable (as are most canopies used for sport parachuting), and have two layers of fabric—top and bottom—connected by airfoil-shaped fabric ribs to form "cells". The cells fill with higher-pressure air from vents that face forward on the leading edge of the airfoil. The fabric is shaped and the parachute lines trimmed under load such that the ballooning fabric inflates into an airfoil shape. This airfoil is sometimes maintained by use of fabric one-way valves called airlocks. "The first jump of this canopy (a Jalbert Parafoil) was made by International Skydiving Hall of Fame member Paul 'Pop' Poppenhager."
Varieties
Personal ram-air parachutes are loosely divided into two varieties – rectangular or tapered – commonly called "squares" or "ellipticals", respectively. Medium-performance canopies (reserve-, BASE-, canopy formation-, and accuracy-type) are usually rectangular. High-performance, ram-air parachutes have a slightly tapered shape to their leading and/or trailing edges when viewed in plan form, and are known as ellipticals. Sometimes all the taper is on the leading edge (front), and sometimes in the trailing edge (tail). | Parachute | Wikipedia | 447 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
Ellipticals are usually used only by sport parachutists. They often have smaller, more numerous fabric cells and are shallower in profile. Their canopies can be anywhere from slightly elliptical to highly elliptical, indicating the amount of taper in the canopy design, which is often an indicator of the responsiveness of the canopy to control input for a given wing loading, and of the level of experience required to pilot the canopy safely.
The rectangular parachute designs tend to look like square, inflatable air mattresses with open front ends. They are generally safer to operate because they are less prone to dive rapidly with relatively small control inputs, they are usually flown with lower wing loadings per square foot of area, and they glide more slowly. They typically have a lower glide ratio.
Wing loading of parachutes is measured similarly to that of aircraft, comparing exit weight to area of parachute fabric. Typical wing loading for students, accuracy competitors, and BASE jumpers is less than 5 kg per square meter – often 0.3 kilograms per square meter or less. Most student skydivers fly with wing loading below 5 kg per square meter. Most sport jumpers fly with wing loading between 5 and 7 kg per square meter, but many interested in performance landings exceed this wing loading. Professional canopy pilots compete with wing loading of 10 to over 15 kilograms per square meter. While ram-air parachutes with wing loading higher than 20 kilograms per square meter have been landed, this is strictly the realm of professional test jumpers.
Smaller parachutes tend to fly faster for the same load, and ellipticals respond faster to control input. Therefore, small, elliptical designs are often chosen by experienced canopy pilots for the thrilling flying they provide. Flying a fast elliptical requires much more skill and experience. Fast ellipticals are also considerably more dangerous to land. With high-performance elliptical canopies, nuisance malfunctions can be much more serious than with a square design, and may quickly escalate into emergencies. Flying highly loaded, elliptical canopies is a major contributing factor in many skydiving accidents, although advanced training programs are helping to reduce this danger.
High-speed, cross-braced parachutes, such as the Velocity, VX, XAOS, and Sensei, have given birth to a new branch of sport parachuting called "swooping." A race course is set up in the landing area for expert pilots to measure the distance they are able to fly past the tall entry gate. Current world records exceed . | Parachute | Wikipedia | 511 | 48339 | https://en.wikipedia.org/wiki/Parachute | Technology | Aviation | null |
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