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Animal Farm | 620 | According to Orwell, Animal Farm reflects events leading up to the Russian Revolution of 1917 and then on into the Stalinist era of the Soviet Union, a period of time when Russia lived under the communist ideology made by Joseph Stalin. Orwell, a democratic socialist, was a critic of Stalin and hostile to Moscow-directed Stalinism, an attitude that was critically shaped by his experiences during the Barcelona May Days conflicts between the POUM and Stalinist forces during the Spanish Civil War. In a letter to Yvonne Davet, Orwell described Animal Farm as a satirical tale against Stalin ("un conte satirique contre Staline"), and in his essay "Why I Write" (1946), wrote that Animal Farm was the first book in which he tried, with full consciousness of what he was doing, "to fuse political purpose and artistic purpose into one whole". |
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Animal Farm | 620 | The original title was Animal Farm: A Fairy Story, but US publishers dropped the subtitle when it was published in 1946, and only one of the translations during Orwell's lifetime, the Telugu version, kept it. Other title variations include subtitles like "A Satire" and "A Contemporary Satire". Orwell suggested the title Union des républiques socialistes animales for the French translation, which abbreviates to URSA, the Latin word for "bear", a symbol of Russia. It also played on the French name of the Soviet Union, Union des républiques socialistes soviétiques. |
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Animal Farm | 620 | Orwell wrote the book between November 1943 and February 1944, when the United Kingdom was in its wartime alliance with the Soviet Union against Nazi Germany, and the British intelligentsia held Stalin in high esteem, a phenomenon Orwell hated. The manuscript was initially rejected by several British and American publishers, including one of Orwell's own, Victor Gollancz, which delayed its publication. It became a great commercial success when it did appear as international relations and public opinion were transformed as the wartime alliance gave way to the Cold War. |
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Animal Farm | 620 | Time magazine chose the book as one of the 100 best English-language novels (1923 to 2005); it also featured at number 31 on the Modern Library List of Best 20th-Century Novels, and number 46 on the BBC's The Big Read poll. It won a Retrospective Hugo Award in 1996 and is included in the Great Books of the Western World selection. |
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Animal Farm | 620 | Plot summary | The animal populace of the poorly run Manor Farm near Willingdon, England, is ripened for rebellion by neglect at the hands of the irresponsible and alcoholic farmer, Mr. Jones. One night, the exalted boar, Old Major, holds a conference, at which he calls for the overthrow of humans and teaches the animals a revolutionary song called "Beasts of England". When Old Major dies, two young pigs, Snowball and Napoleon, assume command and stage a revolt, driving Mr. Jones off the farm and renaming the property "Animal Farm". They adopt the Seven Commandments of Animalism, the most important of which is, "All animals are equal". The decree is painted in large letters on one side of the barn. Snowball teaches the animals to read and write, while Napoleon educates young puppies on the principles of Animalism. To commemorate the start of Animal Farm, Snowball raises a green flag with a white hoof and horn. Food is plentiful, and the farm runs smoothly. The pigs elevate themselves to positions of leadership and set aside special food items, ostensibly for their health. Following an unsuccessful attempt by Mr. Jones and his associates to retake the farm (later dubbed the "Battle of the Cowshed"), Snowball announces his plans to modernise the farm by building a windmill. Napoleon disputes this idea, and matters come to a head, which culminates in Napoleon's dogs chasing Snowball away and Napoleon effectively declaring himself supreme commander. |
Animal Farm | 620 | Plot summary | Napoleon enacts changes to the governance structure of the farm, replacing meetings with a committee of pigs who will run the farm. Through a young porker named Squealer, Napoleon claims credit for the idea of building the windmill, claiming that Snowball was only trying to win animals to his side. The animals work harder with the promise of easier lives with the windmill. When the animals find the windmill collapsed after a violent storm, Napoleon and Squealer persuade the animals that Snowball is trying to sabotage their project, and begin to purge the farm of animals accused by Napoleon of consorting with his old rival. When some animals recall the Battle of the Cowshed, Napoleon (who was nowhere to be found during the battle) gradually smears Snowball to the point of saying he is a collaborator of Mr. Jones, even dismissing the fact that Snowball was given an award of courage while falsely representing himself as the main hero of the battle. "Beasts of England" is replaced with "Animal Farm", while an anthem glorifying Napoleon, who is presumably adopting the lifestyle of a man ("Comrade Napoleon"), is composed and sung. Napoleon then conducts a second purge, during which many animals who are alleged to be helping Snowball in plots are executed by Napoleon's dogs, which troubles the rest of the animals. Despite their hardships, the animals are easily placated by Napoleon's retort that they are better off than they were under Mr. Jones, as well as by the sheep's continual bleating of "four legs good, two legs bad". |
Animal Farm | 620 | Plot summary | Mr. Frederick, a neighbouring farmer, attacks the farm, using blasting powder to blow up the restored windmill. Although the animals win the battle, they do so at great cost, as many, including Boxer the workhorse, are wounded. Although he recovers from this, Boxer eventually collapses while working on the windmill (being almost 12 years old at that point). He is taken away in a knacker's van and a donkey called Benjamin alerts the animals of this, but Squealer quickly waves off their alarm by persuading the animals that the van had been purchased from the knacker by an animal hospital and that the previous owner's signboard had not been repainted. Squealer subsequently reports Boxer's death and honours him with a festival the following day. In truth, Napoleon had engineered the sale of Boxer to the knacker, allowing him and his inner circle to acquire money to buy whisky for themselves. |
Animal Farm | 620 | Plot summary | Years pass, the windmill is rebuilt and another windmill is constructed, which makes the farm a good amount of income. However, the ideals that Snowball discussed, including stalls with electric lighting, heating, and running water, are forgotten, with Napoleon advocating that the happiest animals live simple lives. Snowball has been forgotten, alongside Boxer, with "the exception of the few who knew him". Many of the animals who participated in the rebellion are dead or old. Mr. Jones is also now known to be dead, having "died in an inebriates' home in another part of the country". The pigs start to resemble humans, as they walk upright, carry whips, drink alcohol, and wear clothes. The Seven Commandments are abridged to just one phrase: "All animals are equal, but some animals are more equal than others". The maxim "Four legs good, two legs bad" is similarly changed to "Four legs good, two legs better". Other changes include the Hoof and Horn flag being replaced with a plain green banner and Old Major's skull, which was previously put on display, being reburied. |
Animal Farm | 620 | Plot summary | Napoleon holds a dinner party for the pigs and local farmers, with whom he celebrates a new alliance. He abolishes the practice of the revolutionary traditions and restores the name "The Manor Farm". The men and pigs start playing cards, flattering and praising each other while cheating at the game. Both Napoleon and Mr. Pilkington, one of the farmers, play the Ace of Spades at the same time and both sides begin fighting loudly over who cheated first. When the animals outside look at the pigs and men, they can no longer distinguish between the two. |
Animal Farm | 620 | Genre and style | George Orwell's Animal Farm is an example of a political satire and an allegory that was intended to have a "wider application", according to Orwell himself, in terms of its relevance. Stylistically, the work shares many similarities with some of Orwell's other works, most notably Nineteen Eighty-Four, as both have been considered works of Swiftian satire. Furthermore, these two prominent works seem to suggest Orwell's bleak view of the future for humanity; he seems to stress the potential/current threat of dystopias similar to those in Animal Farm and Nineteen Eighty-Four. In these kinds of works, Orwell distinctly references the disarray and traumatic conditions of Europe following the Second World War. Orwell's style and writing philosophy as a whole were very concerned with the pursuit of truth in writing. |
Animal Farm | 620 | Genre and style | Orwell was committed to communicating straightforwardly, given the way that he felt words were commonly used in politics to deceive and confuse. For this reason, he is careful, in Animal Farm, to make sure the narrator speaks in an unbiased and uncomplicated fashion. The difference is seen in the way that the animals speak and interact, as the general moral animals seem to speak their minds clearly, while the wicked animals on the farm, such as Napoleon, twist language in such a way that it meets their insidious desires. This style reflects Orwell's proximity to the issues facing Europe at the time and his determination to comment critically on Stalin's Soviet Russia. |
Animal Farm | 620 | Background | George Orwell wrote the manuscript between November 1943 and February 1944 after his experiences during the Spanish Civil War, which he described in Homage to Catalonia (1938). In the preface of a 1947 Ukrainian edition of Animal Farm, he explained how escaping the communist purges in Spain taught him "how easily totalitarian propaganda can control the opinion of enlightened people in democratic countries". This motivated Orwell to expose and strongly condemn what he saw as the Stalinist corruption of the original socialist ideals. Homage to Catalonia sold poorly; after seeing Arthur Koestler's best-selling, Darkness at Noon, about the Moscow Trials, Orwell decided that fiction would be the best way to describe totalitarianism. |
Animal Farm | 620 | Background | Immediately before writing the book, Orwell quit the BBC. He was also upset about a booklet for propagandists the Ministry of Information had put out. The booklet included instructions on how to quell ideological fears of the Soviet Union, such as directions to claim that the Red Terror was a figment of Nazi imagination. |
Animal Farm | 620 | Background | In the preface, Orwell described the source of the idea of setting the book on a farm: |
Animal Farm | 620 | Background | I saw a little boy, perhaps ten years old, driving a huge carthorse along a narrow path, whipping it whenever it tried to turn. It struck me that if only such animals became aware of their strength we should have no power over them, and that men exploit animals in much the same way as the rich exploit the proletariat. |
Animal Farm | 620 | Background | In 1944, the manuscript was almost lost when a German V-1 flying bomb destroyed his London home. Orwell spent hours sifting through the rubble to find the pages intact. |
Animal Farm | 620 | Publication | Orwell initially encountered difficulty getting the manuscript published, largely due to fears that the book might upset the alliance between Britain, the United States, and the Soviet Union. Four publishers refused to publish Animal Farm, yet one had initially accepted the work but declined it after consulting the Ministry of Information. Eventually, Secker and Warburg published the first edition in 1945. |
Animal Farm | 620 | Publication | During the Second World War, it became clear to Orwell that anti-Soviet literature was not something which most major publishing houses would touch – including his regular publisher Gollancz. He also submitted the manuscript to Faber and Faber, where the poet T. S. Eliot (who was a director of the firm) rejected it; Eliot wrote back to Orwell praising the book's "good writing" and "fundamental integrity", but declared that they would only accept it for publication if they had some sympathy for the viewpoint "which I take to be generally Trotskyite". Eliot said he found the view "not convincing", and contended that the pigs were made out to be the best to run the farm; he posited that someone might argue "what was needed ... was not more communism but more public-spirited pigs". Orwell let André Deutsch, who was working for Nicholson & Watson in 1944, read the typescript, and Deutsch was convinced that Nicholson & Watson would want to publish it; however, they did not, and "lectured Orwell on what they perceived to be errors in Animal Farm". In his London Letter on 17 April 1944 for Partisan Review, Orwell wrote that it was "now next door to impossible to get anything overtly anti-Russian printed. Anti-Russian books do appear, but mostly from Catholic publishing firms and always from a religious or frankly reactionary angle". |
Animal Farm | 620 | Publication | The publisher Jonathan Cape, who had initially accepted Animal Farm, subsequently rejected the book after an official at the British Ministry of Information warned him off – although the civil servant who it is assumed gave the order was later found to be a Soviet spy. Writing to Leonard Moore, a partner in the literary agency of Christy & Moore, publisher Jonathan Cape explained that the decision had been taken on the advice of a senior official in the Ministry of Information. Such flagrant anti-Soviet bias was unacceptable, and the choice of pigs as the dominant class was thought to be especially offensive. It may reasonably be assumed that the "important official" was a man named Peter Smollett, who was later unmasked as a Soviet agent. Orwell was suspicious of Smollett/Smolka, and he would be one of the names Orwell included in his list of Crypto-Communists and Fellow-Travellers sent to the Information Research Department in 1949. The publisher wrote to Orwell, saying: |
Animal Farm | 620 | Publication | If the fable were addressed generally to dictators and dictatorships at large then publication would be all right, but the fable does follow, as I see now, so completely the progress of the Russian Soviets and their two dictators [Lenin and Stalin], that it can apply only to Russia, to the exclusion of the other dictatorships. |
Animal Farm | 620 | Publication | Another thing: it would be less offensive if the predominant caste in the fable were not pigs. I think the choice of pigs as the ruling caste will no doubt give offence to many people, and particularly to anyone who is a bit touchy, as undoubtedly the Russians are. |
Animal Farm | 620 | Publication | Frederic Warburg also faced pressures against publication, even from people in his own office and from his wife Pamela, who felt that it was not the moment for ingratitude towards Stalin and the Red Army, which had played a major part in defeating Adolf Hitler. A Russian translation was printed in the paper Posev, and in permitting a Russian translation of Animal Farm, Orwell refused in advance all royalties. A translation in Ukrainian, which was produced in Germany, was confiscated in large part by the American wartime authorities and handed over to the Soviet repatriation commission. |
Animal Farm | 620 | Publication | In October 1945, Orwell wrote to Frederic Warburg expressing interest in pursuing the possibility that the political cartoonist David Low might illustrate Animal Farm. Low had written a letter saying that he had had "a good time with Animal Farm – an excellent bit of satire – it would illustrate perfectly". Nothing came of this, and a trial issue produced by Secker & Warburg in 1956 illustrated by John Driver was abandoned. The Folio Society published an edition in 1984 illustrated by Quentin Blake and an edition illustrated by the cartoonist Ralph Steadman was published by Secker & Warburg in 1995 to celebrate the fiftieth anniversary of the first edition of Animal Farm. |
Animal Farm | 620 | Publication | Orwell originally wrote a preface complaining about British self-censorship and how the British people were suppressing criticism of the USSR, their World War II ally: |
Animal Farm | 620 | Publication | The sinister fact about literary censorship in England is that it is largely voluntary ... Things are kept right out of the British press, not because the Government intervenes but because of a general tacit agreement that "it wouldn't do" to mention that particular fact. |
Animal Farm | 620 | Publication | Although the first edition allowed space for the preface, it was not included, and as of June 2009, most editions of the book have not included it. |
Animal Farm | 620 | Publication | Secker and Warburg published the first edition of Animal Farm in 1945, without an introduction. However, the publisher had provided space for a preface in the author's proof composited from the manuscript. For reasons unknown, no preface was supplied, and the page numbers had to be renumbered at the last minute. |
Animal Farm | 620 | Publication | In 1972, Ian Angus found the original typescript titled "The Freedom of the Press", and Bernard Crick published it, together with his introduction, in The Times Literary Supplement on 15 September 1972 as "How the essay came to be written". Orwell's essay criticised British self-censorship by the press, specifically the suppression of unflattering descriptions of Stalin and the Soviet government. The same essay also appeared in the Italian 1976 edition of Animal Farm with another introduction by Crick, claiming to be the first edition with the preface. Other publishers were still declining to publish it. |
Animal Farm | 620 | Reception | Contemporary reviews of the work were not universally positive. Writing in the American The New Republic magazine, George Soule expressed his disappointment in the book, writing that it "puzzled and saddened me. It seemed on the whole dull. The allegory turned out to be a creaking machine for saying in a clumsy way things that have been said better directly". Soule believed that the animals were not consistent enough with their real-world inspirations, and said, "It seems to me that the failure of this book (commercially it is already assured of tremendous success) arises from the fact that the satire deals not with something the author has experienced, but rather with stereotyped ideas about a country which he probably does not know very well". |
Animal Farm | 620 | Reception | The Guardian on 24 August 1945 called Animal Farm "a delightfully humorous and caustic satire on the rule of the many by the few". Tosco Fyvel, writing in Tribune on the same day, called the book "a gentle satire on a certain State and on the illusions of an age which may already be behind us". Julian Symons responded, on 7 September, "Should we not expect, in Tribune at least, acknowledgement of the fact that it is a satire not at all gentle upon a particular State – Soviet Russia? It seems to me that a reviewer should have the courage to identify Napoleon with Stalin, and Snowball with Trotsky, and express an opinion favourable or unfavourable to the author, upon a political ground. In a hundred years perhaps, Animal Farm may be simply a fairy story; today it is a political satire with a good deal of point". Animal Farm has been subject to much comment in the decades since these early remarks. |
Animal Farm | 620 | Reception | Between 1952 and 1957, the CIA, in an operation codenamed Aedinosaur, sent millions of balloons carrying copies of the novel into Poland, Hungary and Czechoslovakia, whose air forces tried to shoot the balloons down. |
Animal Farm | 620 | Reception | Time magazine chose Animal Farm as one of the 100 best English-language novels (1923 to 2005); it also featured at number 31 on the Modern Library List of Best 20th-Century Novels. It won a Retrospective Hugo Award in 1996 and is included in the Great Books of the Western World selection. |
Animal Farm | 620 | Reception | Popular reading in schools, Animal Farm was ranked the UK's favourite book from school in a 2016 poll. |
Animal Farm | 620 | Reception | Animal Farm has also faced an array of challenges in school settings around the US. The following are examples of this controversy that has existed around Orwell's work: |
Animal Farm | 620 | Reception | Animal Farm has also faced similar forms of resistance in other countries. The ALA also mentions the way that the book was prevented from being featured at the International Book Fair in Moscow, Russia, in 1977 and banned from schools in the United Arab Emirates for references to practices or actions that defy Arab or Islamic beliefs, such as pigs or alcohol. |
Animal Farm | 620 | Reception | In the same manner, Animal Farm has also faced relatively recent issues in China. In 2018, the government decided to censor all online posts about or referring to Animal Farm. However, the book itself, as of 2019, remains sold in stores. Amy Hawkins and Jeffrey Wasserstrom of The Atlantic stated in 2019 that the book is widely available in Mainland China for several reasons: censors believe the general public is unlikely to read a highbrow book, because the elites who do read books feel connected to the ruling party anyway, and because the Communist Party sees being too aggressive in blocking cultural products as a liability. The authors stated: "It was – and remains – as easy to buy 1984 and Animal Farm in Shenzhen or Shanghai as it is in London or Los Angeles". An enhanced version of the book, launched in India in 2017, was widely praised for capturing the author's intent, by republishing the proposed preface of the First Edition and the preface he wrote for the Ukrainian edition. |
Animal Farm | 620 | Analysis | Snowball, Napoleon, and Squealer adapt Old Major's ideas into "a complete system of thought", which they formally name Animalism, an allegoric reference to Communism, not to be confused with the philosophy of Animalism. Soon after, Napoleon and Squealer partake in activities associated with the humans (drinking alcohol, sleeping in beds, trading), which were explicitly prohibited by the Seven Commandments. Squealer is employed to alter the Seven Commandments to account for this humanisation, an allusion to the Soviet government's revising of history to exercise control of the people's beliefs about themselves and their society. |
Animal Farm | 620 | Analysis | The original commandments are: |
Animal Farm | 620 | Analysis | These commandments are also distilled into the maxim "Four legs good, two legs bad!" which is primarily used by the sheep on the farm, often to disrupt discussions and disagreements between animals on the nature of Animalism. |
Animal Farm | 620 | Analysis | Later, Napoleon and his pigs secretly revise some commandments to clear themselves of accusations of law-breaking. The changed commandments are as follows, with the changes bolded: |
Animal Farm | 620 | Analysis | Eventually, these are replaced with the maxims, "All animals are equal, but some animals are more equal than others", and "Four legs good, two legs better" as the pigs become more anthropomorphic. This is an ironic twist to the original purpose of the Seven Commandments, which was supposed to keep order within Animal Farm by uniting the animals together against the humans and preventing animals from following the humans' evil habits. Through the revision of the commandments, Orwell demonstrates how simply political dogma can be turned into malleable propaganda. |
Animal Farm | 620 | Analysis | Orwell biographer Jeffrey Meyers has written, "virtually every detail has political significance in this allegory". Orwell himself wrote in 1946, "Of course I intended it primarily as a satire on the Russian revolution ... [and] that kind of revolution (violent conspiratorial revolution, led by unconsciously power-hungry people) can only lead to a change of masters [–] revolutions only effect a radical improvement when the masses are alert". In a preface for a 1947 Ukrainian edition, he stated, "for the past ten years I have been convinced that the destruction of the Soviet myth was essential if we wanted a revival of the socialist movement. On my return from Spain [in 1937] I thought of exposing the Soviet myth in a story that could be easily understood by almost anyone and which could be easily translated into other languages". |
Animal Farm | 620 | Analysis | The revolt of the animals against Farmer Jones is Orwell's analogy with the October 1917 Bolshevik Revolution. The Battle of the Cowshed has been said to represent the allied invasion of Soviet Russia in 1918, and the defeat of the White Russians in the Russian Civil War. The pigs' rise to preeminence mirrors the rise of a Stalinist bureaucracy in the USSR, just as Napoleon's emergence as the farm's sole leader reflects Stalin's emergence. The pigs' appropriation of milk and apples for their own use, "the turning point of the story" as Orwell termed it in a letter to Dwight Macdonald, stands as an analogy for the crushing of the left-wing 1921 Kronstadt revolt against the Bolsheviks, and the difficult efforts of the animals to build the windmill suggest the various Five Year Plans. The puppies controlled by Napoleon parallel the nurture of the secret police in the Stalinist structure, and the pigs' treatment of the other animals on the farm recalls the internal terror faced by the populace in the 1930s. In chapter seven, when the animals confess their non-existent crimes and are killed, Orwell directly alludes to the purges, confessions and show trials of the late 1930s. These contributed to Orwell's conviction that the Bolshevik revolution had been corrupted and the Soviet system become rotten. |
Animal Farm | 620 | Analysis | Peter Edgerly Firchow and Peter Davison contend that the Battle of the Windmill, specifically referencing the Battle of Stalingrad and the Battle of Moscow, represents World War II. During the battle, Orwell first wrote, "All the animals, including Napoleon" took cover. Orwell had the publisher alter this to "All the animals except Napoleon" in recognition of Stalin's decision to remain in Moscow during the German advance. Orwell requested the change after he met Józef Czapski in Paris in March 1945. Czapski, a survivor of the Katyn Massacre and an opponent of the Soviet regime, told Orwell, as Orwell wrote to Arthur Koestler, that it had been "the character [and] greatness of Stalin" that saved Russia from the German invasion. |
Animal Farm | 620 | Analysis | Other connections that writers have suggested illustrate Orwell's telescoping of Russian history from 1917 to 1943, including the wave of rebelliousness that ran through the countryside after the Rebellion, which stands for the abortive revolutions in Hungary and Germany (Ch. IV); the conflict between Napoleon and Snowball (Ch. V), parallelling "the two rival and quasi-Messianic beliefs that seemed pitted against one another: Trotskyism, with its faith in the revolutionary vocation of the proletariat of the West; and Stalinism with its glorification of Russia's socialist destiny"; Napoleon's dealings with Whymper and the Willingdon markets (Ch. VI), paralleling the Treaty of Rapallo; and Frederick's forged bank notes, parallelling the Hitler-Stalin pact of August 1939, after which Frederick attacks Animal Farm without warning and destroys the windmill. |
Animal Farm | 620 | Analysis | The book's close, with the pigs and men in a kind of rapprochement, reflected Orwell's view of the 1943 Tehran Conference that seemed to display the establishment of "the best possible relations between the USSR and the West" – but in reality were destined, as Orwell presciently predicted, to continue to unravel. The disagreement between the allies and the start of the Cold War is suggested when Napoleon and Pilkington, both suspicious, each "played an ace of spades simultaneously". |
Animal Farm | 620 | Analysis | Similarly, the music in the novel, starting with "Beasts of England" and the later anthems, parallels "The Internationale" and its adoption and repudiation by the Soviet authorities as the anthem of the USSR in the 1920s and 1930s. |
Animal Farm | 620 | Analysis | According to Masha Gessen, the metamorphosis of the eighth commandment ("some animals are more equal") was likely inspired by similar change of a party line which declared all Soviet people equal: the Russian nation and language suddenly became "first among equals" in official CPSU publications in 1936–1937. |
Animal Farm | 620 | Adaptations | A theatrical version, with music by Richard Peaslee and lyrics by Adrian Mitchell, was staged at the National Theatre London on 25 April 1984, directed by Peter Hall. It toured nine cities in 1985. |
Animal Farm | 620 | Adaptations | A solo version, adapted and performed by Guy Masterson, premiered at the Traverse Theatre Edinburgh in January 1995 and has toured worldwide since. |
Animal Farm | 620 | Adaptations | In 2021, during pandemic restrictions, the National Youth Theatre toured a stage version of Animal Farm; this run included outdoor performances on a farm at Soulton Hall. |
Animal Farm | 620 | Adaptations | A new adaptation written and directed by Robert Icke, designed by Bunny Christie with puppetry designed and directed by Toby Olié opened at the Birmingham Repertory Theatre in January 2022 before touring the UK. |
Animal Farm | 620 | Adaptations | Animal Farm has been adapted to film twice. Both differ from the novel and have been accused of taking significant liberties, including sanitising some aspects. |
Animal Farm | 620 | Adaptations | Andy Serkis is directing an upcoming animated film adaptation. |
Animal Farm | 620 | Adaptations | A BBC radio version, produced by Rayner Heppenstall, was broadcast in January 1947. Orwell listened to the production at his home in Canonbury Square, London, with Hugh Gordon Porteous, amongst others. Orwell later wrote to Heppenstall that Porteous, "who had not read the book, grasped what was happening after a few minutes". |
Animal Farm | 620 | Adaptations | A further radio production, again using Orwell's dramatisation of the book, was broadcast in January 2013 on BBC Radio 4. Tamsin Greig narrated, and the cast included Nicky Henson as Napoleon, Toby Jones as the propagandist Squealer, and Ralph Ineson as Boxer. |
Animal Farm | 620 | Adaptations | In 1950, Norman Pett and his writing partner Don Freeman were secretly hired by the Information Research Department, a secret department of the Foreign Office, to adapt Animal Farm into a comic strip. This comic was not published in the United Kingdom but ran in Brazilian and Burmese newspapers. |
Amphibian | 621 | Amphibians are ectothermic, anamniotic, four-limbed vertebrate animals that constitute the class Amphibia. In its broad sense, it is paraphyletic group encompassing all tetrapods excluding the amniotes (tetrapods with an amniotic membrane, such as modern reptiles, birds, and mammals). All extant (living) amphibians belong to the monophyletic subclass Lissamphibia, with three living orders: Anura (frogs), Urodela (salamanders), and Gymnophiona (caecilians). Evolved to be mostly semiaquatic, amphibians have adapted to inhabit a wide variety of habitats, with most species living in freshwater, wetland or terrestrial ecosystems (such as riparian woodland, fossorial and even arboreal habitats). Their life cycle typically starts out as aquatic larvae with gills known as tadpoles, but some species have developed behavioural adaptations to bypass this. |
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Amphibian | 621 | The young generally undergo metamorphosis from larva with gills to an adult air-breathing form with lungs. Amphibians use their skin as a secondary respiratory surface and some small terrestrial salamanders and frogs lack lungs and rely entirely on their skin. They are superficially similar to reptiles like lizards, but unlike reptiles and other amniotes, require water bodies in which to breed. With their complex reproductive needs and permeable skins, amphibians are often ecological indicators; in recent decades there has been a dramatic decline in amphibian populations for many species around the globe. |
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Amphibian | 621 | The earliest amphibians evolved in the Devonian period from sarcopterygian fish with lungs and bony-limbed fins, features that were helpful in adapting to dry land. They diversified and became ecologically dominant during the Carboniferous and Permian periods, but were later displaced in terrestrial environments by early reptiles and basal synapsids (mammal predecessors). The origin of modern amphibians belonging to Lissamphibia, which first appeared during the Early Triassic, around 250 million years ago, has long been contentious. However the emerging consensus is that they likely originated from temnospondyls, the most diverse group of prehistoric amphibians, during the Permian period. |
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Amphibian | 621 | A fourth group of lissamphibians, the Albanerpetontidae, became extinct around 2 million years ago. The number of known amphibian species is approximately 8,000, of which nearly 90% are frogs. The smallest amphibian (and vertebrate) in the world is a frog from New Guinea (Paedophryne amauensis) with a length of just 7.7 mm (0.30 in). The largest living amphibian is the 1.8 m (5 ft 11 in) South China giant salamander (Andrias sligoi), but this is dwarfed by prehistoric temnospondyls such as Mastodonsaurus which could reach up to 6 m (20 ft) in length. The study of amphibians is called batrachology, while the study of both reptiles and amphibians is called herpetology. |
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Amphibian | 621 | Classification | The word amphibian is derived from the Ancient Greek term ἀμφίβιος (amphíbios), which means 'both kinds of life', ἀμφί meaning 'of both kinds' and βιος meaning 'life'. The term was initially used as a general adjective for animals that could live on land or in water, including seals and otters. Traditionally, the class Amphibia includes all tetrapod vertebrates that are not amniotes. Amphibia in its widest sense (sensu lato) was divided into three subclasses, two of which are extinct: |
Amphibian | 621 | Classification | These three subclasses do not include all extinct amphibians. Other extinct amphibian groups include Embolomeri (Late Paleozoic large aquatic predators), Seymouriamorpha (semiaquatic to terrestrial Permian forms related to amniotes), among others. Names such as Tetrapoda and Stegocephalia encompass the entirety of amphibian-grade tetrapods, while Reptiliomorpha or Anthracosauria are variably used to describe extinct amphibians more closely related to amniotes than to lissamphibians. |
Amphibian | 621 | Classification | The actual number of species in each group depends on the taxonomic classification followed. The two most common systems are the classification adopted by the website AmphibiaWeb, University of California, Berkeley, and the classification by herpetologist Darrel Frost and the American Museum of Natural History, available as the online reference database "Amphibian Species of the World". The numbers of species cited above follows Frost and the total number of known (living) amphibian species as of March 31, 2019, is exactly 8,000, of which nearly 90% are frogs. |
Amphibian | 621 | Classification | With the phylogenetic classification, the taxon Labyrinthodontia has been discarded as it is a polyparaphyletic group without unique defining features apart from shared primitive characteristics. Classification varies according to the preferred phylogeny of the author and whether they use a stem-based or a node-based classification. Traditionally, amphibians as a class are defined as all tetrapods with a larval stage, while the group that includes the common ancestors of all living amphibians (frogs, salamanders and caecilians) and all their descendants is called Lissamphibia. The phylogeny of Paleozoic amphibians is uncertain, and Lissamphibia may possibly fall within extinct groups, like the Temnospondyli (traditionally placed in the subclass Labyrinthodontia) or the Lepospondyli, and in some analyses even in the amniotes. This means that advocates of phylogenetic nomenclature have removed a large number of basal Devonian and Carboniferous amphibian-type tetrapod groups that were formerly placed in Amphibia in Linnaean taxonomy, and included them elsewhere under cladistic taxonomy. If the common ancestor of amphibians and amniotes is included in Amphibia, it becomes a paraphyletic group. |
Amphibian | 621 | Classification | All modern amphibians are included in the subclass Lissamphibia, which is usually considered a clade, a group of species that have evolved from a common ancestor. The three modern orders are Anura (the frogs), Caudata (or Urodela, the salamanders), and Gymnophiona (or Apoda, the caecilians). It has been suggested that salamanders arose separately from a temnospondyl-like ancestor, and even that caecilians are the sister group of the advanced reptiliomorph amphibians, and thus of amniotes. Although the fossils of several older proto-frogs with primitive characteristics are known, the oldest "true frog", with hopping adaptations is Prosalirus bitis, from the Early Jurassic Kayenta Formation of Arizona. It is anatomically very similar to modern frogs. The oldest known caecilians are Funcusvermis gilmorei (from the Late Triassic) and Eocaecilia micropodia (from the Early Jurassic), both from Arizona. The earliest salamander is Beiyanerpeton jianpingensis from the Late Jurassic of northeastern China. |
Amphibian | 621 | Classification | Authorities disagree as to whether Salientia is a superorder that includes the order Anura, or whether Anura is a sub-order of the order Salientia. The Lissamphibia are traditionally divided into three orders, but an extinct salamander-like family, the Albanerpetontidae, is now considered part of Lissamphibia alongside the superorder Salientia. Furthermore, Salientia includes all three recent orders plus the Triassic proto-frog, Triadobatrachus. |
Amphibian | 621 | Evolutionary history | The first major groups of amphibians developed in the Devonian period, around 370 million years ago, from lobe-finned fish which were similar to the modern coelacanth and lungfish. These ancient lobe-finned fish had evolved multi-jointed leg-like fins with digits that enabled them to crawl along the sea bottom. Some fish had developed primitive lungs that help them breathe air when the stagnant pools of the Devonian swamps were low in oxygen. They could also use their strong fins to hoist themselves out of the water and onto dry land if circumstances so required. Eventually, their bony fins would evolve into limbs and they would become the ancestors to all tetrapods, including modern amphibians, reptiles, birds, and mammals. Despite being able to crawl on land, many of these prehistoric tetrapodomorph fish still spent most of their time in the water. They had started to develop lungs, but still breathed predominantly with gills. |
Amphibian | 621 | Evolutionary history | Many examples of species showing transitional features have been discovered. Ichthyostega was one of the first primitive amphibians, with nostrils and more efficient lungs. It had four sturdy limbs, a neck, a tail with fins and a skull very similar to that of the lobe-finned fish, Eusthenopteron. Amphibians evolved adaptations that allowed them to stay out of the water for longer periods. Their lungs improved and their skeletons became heavier and stronger, better able to support the weight of their bodies on land. They developed "hands" and "feet" with five or more digits; the skin became more capable of retaining body fluids and resisting desiccation. The fish's hyomandibula bone in the hyoid region behind the gills diminished in size and became the stapes of the amphibian ear, an adaptation necessary for hearing on dry land. An affinity between the amphibians and the teleost fish is the multi-folded structure of the teeth and the paired supra-occipital bones at the back of the head, neither of these features being found elsewhere in the animal kingdom. |
Amphibian | 621 | Evolutionary history | At the end of the Devonian period (360 million years ago), the seas, rivers and lakes were teeming with life while the land was the realm of early plants and devoid of vertebrates, though some, such as Ichthyostega, may have sometimes hauled themselves out of the water. It is thought they may have propelled themselves with their forelimbs, dragging their hindquarters in a similar manner to that used by the elephant seal. In the early Carboniferous (360 to 323 million years ago), the climate was relatively wet and warm. Extensive swamps developed with mosses, ferns, horsetails and calamites. Air-breathing arthropods evolved and invaded the land where they provided food for the carnivorous amphibians that began to adapt to the terrestrial environment. There were no other tetrapods on the land and the amphibians were at the top of the food chain, with some occupying ecological positions currently held by crocodiles. Though equipped with limbs and the ability to breathe air, most still had a long tapering body and strong tail. Others were the top land predators, sometimes reaching several metres in length, preying on the large insects of the period and the many types of fish in the water. They still needed to return to water to lay their shell-less eggs, and even most modern amphibians have a fully aquatic larval stage with gills like their fish ancestors. It was the development of the amniotic egg, which prevents the developing embryo from drying out, that enabled the reptiles to reproduce on land and which led to their dominance in the period that followed. |
Amphibian | 621 | Evolutionary history | After the Carboniferous rainforest collapse amphibian dominance gave way to reptiles, and amphibians were further devastated by the Permian–Triassic extinction event. During the Triassic Period (252 to 201 million years ago), the reptiles continued to out-compete the amphibians, leading to a reduction in both the amphibians' size and their importance in the biosphere. According to the fossil record, Lissamphibia, which includes all modern amphibians and is the only surviving lineage, may have branched off from the extinct groups Temnospondyli and Lepospondyli at some period between the Late Carboniferous and the Early Triassic. The relative scarcity of fossil evidence precludes precise dating, but the most recent molecular study, based on multilocus sequence typing, suggests a Late Carboniferous/Early Permian origin for extant amphibians. |
Amphibian | 621 | Evolutionary history | The origins and evolutionary relationships between the three main groups of amphibians is a matter of debate. A 2005 molecular phylogeny, based on rDNA analysis, suggests that salamanders and caecilians are more closely related to each other than they are to frogs. It also appears that the divergence of the three groups took place in the Paleozoic or early Mesozoic (around 250 million years ago), before the breakup of the supercontinent Pangaea and soon after their divergence from the lobe-finned fish. The briefness of this period, and the swiftness with which radiation took place, would help account for the relative scarcity of primitive amphibian fossils. There are large gaps in the fossil record, the discovery of the dissorophoid temnospondyl Gerobatrachus from the Early Permian in Texas in 2008 provided a missing link with many of the characteristics of modern frogs. Molecular analysis suggests that the frog–salamander divergence took place considerably earlier than the palaeontological evidence indicates. One study suggested suggested that the last common ancestor of all modern amphibians lived about 315 million years ago, and that stereospondyl temnospondyls are the closest relatives to the caecilians. However, most studies support a single monophyletic origin of all modern amphibians within the dissorophoid temnospondyls. |
Amphibian | 621 | Evolutionary history | As they evolved from lunged fish, amphibians had to make certain adaptations for living on land, including the need to develop new means of locomotion. In the water, the sideways thrusts of their tails had propelled them forward, but on land, quite different mechanisms were required. Their vertebral columns, limbs, limb girdles and musculature needed to be strong enough to raise them off the ground for locomotion and feeding. Terrestrial adults discarded their lateral line systems and adapted their sensory systems to receive stimuli via the medium of the air. They needed to develop new methods to regulate their body heat to cope with fluctuations in ambient temperature. They developed behaviours suitable for reproduction in a terrestrial environment. Their skins were exposed to harmful ultraviolet rays that had previously been absorbed by the water. The skin changed to become more protective and prevent excessive water loss. |
Amphibian | 621 | Characteristics | The superclass Tetrapoda is divided into four classes of vertebrate animals with four limbs. Reptiles, birds and mammals are amniotes, the eggs of which are either laid or carried by the female and are surrounded by several membranes, some of which are impervious. Lacking these membranes, amphibians require water bodies for reproduction, although some species have developed various strategies for protecting or bypassing the vulnerable aquatic larval stage. They are not found in the sea with the exception of one or two frogs that live in brackish water in mangrove swamps; the Anderson's salamander meanwhile occurs in brackish or salt water lakes. On land, amphibians are restricted to moist habitats because of the need to keep their skin damp. |
Amphibian | 621 | Characteristics | Modern amphibians have a simplified anatomy compared to their ancestors due to paedomorphosis, caused by two evolutionary trends: miniaturization and an unusually large genome, which result in a slower growth and development rate compared to other vertebrates. Another reason for their size is associated with their rapid metamorphosis, which seems to have evolved only in the ancestors of lissamphibia; in all other known lines the development was much more gradual. Because a remodeling of the feeding apparatus means they do not eat during the metamorphosis, the metamorphosis has to go faster the smaller the individual is, so it happens at an early stage when the larvae are still small. (The largest species of salamanders do not go through a metamorphosis.) Amphibians that lay eggs on land often go through the whole metamorphosis inside the egg. An anamniotic terrestrial egg is less than 1 cm in diameter due to diffusion problems, a size which puts a limit on the amount of posthatching growth. |
Amphibian | 621 | Characteristics | The smallest amphibian (and vertebrate) in the world is a microhylid frog from New Guinea (Paedophryne amauensis) first discovered in 2012. It has an average length of 7.7 mm (0.30 in) and is part of a genus that contains four of the world's ten smallest frog species. The largest living amphibian is the 1.8 m (5 ft 11 in) Chinese giant salamander (Andrias davidianus) but this is a great deal smaller than the largest amphibian that ever existed—the extinct 9 m (30 ft) Prionosuchus, a crocodile-like temnospondyl dating to 270 million years ago from the middle Permian of Brazil. The largest frog is the African Goliath frog (Conraua goliath), which can reach 32 cm (13 in) and weigh 3 kg (6.6 lb). |
Amphibian | 621 | Characteristics | Amphibians are ectothermic (cold-blooded) vertebrates that do not maintain their body temperature through internal physiological processes. Their metabolic rate is low and as a result, their food and energy requirements are limited. In the adult state, they have tear ducts and movable eyelids, and most species have ears that can detect airborne or ground vibrations. They have muscular tongues, which in many species can be protruded. Modern amphibians have fully ossified vertebrae with articular processes. Their ribs are usually short and may be fused to the vertebrae. Their skulls are mostly broad and short, and are often incompletely ossified. Their skin contains little keratin and lacks scales, apart from a few fish-like scales in certain caecilians. The skin contains many mucous glands and in some species, poison glands (a type of granular gland). The hearts of amphibians have three chambers, two atria and one ventricle. They have a urinary bladder and nitrogenous waste products are excreted primarily as urea. Most amphibians lay their eggs in water and have aquatic larvae that undergo metamorphosis to become terrestrial adults. Amphibians breathe by means of a pump action in which air is first drawn into the buccopharyngeal region through the nostrils. These are then closed and the air is forced into the lungs by contraction of the throat. They supplement this with gas exchange through the skin. |
Amphibian | 621 | Characteristics | The order Anura (from the Ancient Greek a(n)- meaning "without" and oura meaning "tail") comprises the frogs and toads. They usually have long hind limbs that fold underneath them, shorter forelimbs, webbed toes with no claws, no tails, large eyes and glandular moist skin. Members of this order with smooth skins are commonly referred to as frogs, while those with warty skins are known as toads. The difference is not a formal one taxonomically and there are numerous exceptions to this rule. Members of the family Bufonidae are known as the "true toads". Frogs range in size from the 30-centimetre (12 in) Goliath frog (Conraua goliath) of West Africa to the 7.7-millimetre (0.30 in) Paedophryne amauensis, first described in Papua New Guinea in 2012, which is also the smallest known vertebrate. Although most species are associated with water and damp habitats, some are specialised to live in trees or in deserts. They are found worldwide except for polar areas. |
Amphibian | 621 | Characteristics | Anura is divided into three suborders that are broadly accepted by the scientific community, but the relationships between some families remain unclear. Future molecular studies should provide further insights into their evolutionary relationships. The suborder Archaeobatrachia contains four families of primitive frogs. These are Ascaphidae, Bombinatoridae, Discoglossidae and Leiopelmatidae which have few derived features and are probably paraphyletic with regard to other frog lineages. The six families in the more evolutionarily advanced suborder Mesobatrachia are the fossorial Megophryidae, Pelobatidae, Pelodytidae, Scaphiopodidae and Rhinophrynidae and the obligatorily aquatic Pipidae. These have certain characteristics that are intermediate between the two other suborders. Neobatrachia is by far the largest suborder and includes the remaining families of modern frogs, including most common species. Ninety-six percent of the over 5,000 extant species of frog are neobatrachians. |
Amphibian | 621 | Characteristics | The order Caudata (from the Latin cauda meaning "tail") consists of the salamanders—elongated, low-slung animals that mostly resemble lizards in form. This is a symplesiomorphic trait and they are no more closely related to lizards than they are to mammals. Salamanders lack claws, have scale-free skins, either smooth or covered with tubercles, and tails that are usually flattened from side to side and often finned. They range in size from the Chinese giant salamander (Andrias davidianus), which has been reported to grow to a length of 1.8 metres (5 ft 11 in), to the diminutive Thorius pennatulus from Mexico which seldom exceeds 20 mm (0.8 in) in length. Salamanders have a mostly Laurasian distribution, being present in much of the Holarctic region of the northern hemisphere. The family Plethodontidae is also found in Central America and South America north of the Amazon basin; South America was apparently invaded from Central America by about the start of the Miocene, 23 million years ago. Urodela is a name sometimes used for all the extant species of salamanders. Members of several salamander families have become paedomorphic and either fail to complete their metamorphosis or retain some larval characteristics as adults. Most salamanders are under 15 cm (6 in) long. They may be terrestrial or aquatic and many spend part of the year in each habitat. When on land, they mostly spend the day hidden under stones or logs or in dense vegetation, emerging in the evening and night to forage for worms, insects and other invertebrates. |
Amphibian | 621 | Characteristics | The suborder Cryptobranchoidea contains the primitive salamanders. A number of fossil cryptobranchids have been found, but there are only three living species, the Chinese giant salamander (Andrias davidianus), the Japanese giant salamander (Andrias japonicus) and the hellbender (Cryptobranchus alleganiensis) from North America. These large amphibians retain several larval characteristics in their adult state; gills slits are present and the eyes are unlidded. A unique feature is their ability to feed by suction, depressing either the left side of their lower jaw or the right. The males excavate nests, persuade females to lay their egg strings inside them, and guard them. As well as breathing with lungs, they respire through the many folds in their thin skin, which has capillaries close to the surface. |
Amphibian | 621 | Characteristics | The suborder Salamandroidea contains the advanced salamanders. They differ from the cryptobranchids by having fused prearticular bones in the lower jaw, and by using internal fertilisation. In salamandrids, the male deposits a bundle of sperm, the spermatophore, and the female picks it up and inserts it into her cloaca where the sperm is stored until the eggs are laid. The largest family in this group is Plethodontidae, the lungless salamanders, which includes 60% of all salamander species. The family Salamandridae includes the true salamanders and the name "newt" is given to members of its subfamily Pleurodelinae. |
Amphibian | 621 | Characteristics | The third suborder, Sirenoidea, contains the four species of sirens, which are in a single family, Sirenidae. Members of this order are eel-like aquatic salamanders with much reduced forelimbs and no hind limbs. Some of their features are primitive while others are derived. Fertilisation is likely to be external as sirenids lack the cloacal glands used by male salamandrids to produce spermatophores and the females lack spermathecae for sperm storage. Despite this, the eggs are laid singly, a behaviour not conducive for external fertilisation. |
Amphibian | 621 | Characteristics | The order Gymnophiona (from the Greek gymnos meaning "naked" and ophis meaning "serpent") or Apoda comprises the caecilians. These are long, cylindrical, limbless animals with a snake- or worm-like form. The adults vary in length from 8 to 75 centimetres (3 to 30 inches) with the exception of Thomson's caecilian (Caecilia thompsoni), which can reach 150 centimetres (4.9 feet). A caecilian's skin has a large number of transverse folds and in some species contains tiny embedded dermal scales. It has rudimentary eyes covered in skin, which are probably limited to discerning differences in light intensity. It also has a pair of short tentacles near the eye that can be extended and which have tactile and olfactory functions. Most caecilians live underground in burrows in damp soil, in rotten wood and under plant debris, but some are aquatic. Most species lay their eggs underground and when the larvae hatch, they make their way to adjacent bodies of water. Others brood their eggs and the larvae undergo metamorphosis before the eggs hatch. A few species give birth to live young, nourishing them with glandular secretions while they are in the oviduct. Caecilians have a mostly Gondwanan distribution, being found in tropical regions of Africa, Asia and Central and South America. |
Amphibian | 621 | Anatomy and physiology | The integumentary structure contains some typical characteristics common to terrestrial vertebrates, such as the presence of highly cornified outer layers, renewed periodically through a moulting process controlled by the pituitary and thyroid glands. Local thickenings (often called warts) are common, such as those found on toads. The outside of the skin is shed periodically mostly in one piece, in contrast to mammals and birds where it is shed in flakes. Amphibians often eat the sloughed skin. Caecilians are unique among amphibians in having mineralized dermal scales embedded in the dermis between the furrows in the skin. The similarity of these to the scales of bony fish is largely superficial. Lizards and some frogs have somewhat similar osteoderms forming bony deposits in the dermis, but this is an example of convergent evolution with similar structures having arisen independently in diverse vertebrate lineages. |
Amphibian | 621 | Anatomy and physiology | Amphibian skin is permeable to water. Gas exchange can take place through the skin (cutaneous respiration) and this allows adult amphibians to respire without rising to the surface of water and to hibernate at the bottom of ponds. To compensate for their thin and delicate skin, amphibians have evolved mucous glands, principally on their heads, backs and tails. The secretions produced by these help keep the skin moist. In addition, most species of amphibian have granular glands that secrete distasteful or poisonous substances. Some amphibian toxins can be lethal to humans while others have little effect. The main poison-producing glands, the parotoids, produce the neurotoxin bufotoxin and are located behind the ears of toads, along the backs of frogs, behind the eyes of salamanders and on the upper surface of caecilians. |
Amphibian | 621 | Anatomy and physiology | The skin colour of amphibians is produced by three layers of pigment cells called chromatophores. These three cell layers consist of the melanophores (occupying the deepest layer), the guanophores (forming an intermediate layer and containing many granules, producing a blue-green colour) and the lipophores (yellow, the most superficial layer). The colour change displayed by many species is initiated by hormones secreted by the pituitary gland. Unlike bony fish, there is no direct control of the pigment cells by the nervous system, and this results in the colour change taking place more slowly than happens in fish. A vividly coloured skin usually indicates that the species is toxic and is a warning sign to predators. |
Amphibian | 621 | Anatomy and physiology | Amphibians have a skeletal system that is structurally homologous to other tetrapods, though with a number of variations. They all have four limbs except for the legless caecilians and a few species of salamander with reduced or no limbs. The bones are hollow and lightweight. The musculoskeletal system is strong to enable it to support the head and body. The bones are fully ossified and the vertebrae interlock with each other by means of overlapping processes. The pectoral girdle is supported by muscle, and the well-developed pelvic girdle is attached to the backbone by a pair of sacral ribs. The ilium slopes forward and the body is held closer to the ground than is the case in mammals. |
Amphibian | 621 | Anatomy and physiology | In most amphibians, there are four digits on the fore foot and five on the hind foot, but no claws on either. Some salamanders have fewer digits and the amphiumas are eel-like in appearance with tiny, stubby legs. The sirens are aquatic salamanders with stumpy forelimbs and no hind limbs. The caecilians are limbless. They burrow in the manner of earthworms with zones of muscle contractions moving along the body. On the surface of the ground or in water they move by undulating their body from side to side. |
Amphibian | 621 | Anatomy and physiology | In frogs, the hind legs are larger than the fore legs, especially so in those species that principally move by jumping or swimming. In the walkers and runners the hind limbs are not so large, and the burrowers mostly have short limbs and broad bodies. The feet have adaptations for the way of life, with webbing between the toes for swimming, broad adhesive toe pads for climbing, and keratinised tubercles on the hind feet for digging (frogs usually dig backwards into the soil). In most salamanders, the limbs are short and more or less the same length and project at right angles from the body. Locomotion on land is by walking and the tail often swings from side to side or is used as a prop, particularly when climbing. In their normal gait, only one leg is advanced at a time in the manner adopted by their ancestors, the lobe-finned fish. Some salamanders in the genus Aneides and certain plethodontids climb trees and have long limbs, large toepads and prehensile tails. In aquatic salamanders and in frog tadpoles, the tail has dorsal and ventral fins and is moved from side to side as a means of propulsion. Adult frogs do not have tails and caecilians have only very short ones. |
Amphibian | 621 | Anatomy and physiology | Salamanders use their tails in defence and some are prepared to jettison them to save their lives in a process known as autotomy. Certain species in the Plethodontidae have a weak zone at the base of the tail and use this strategy readily. The tail often continues to twitch after separation which may distract the attacker and allow the salamander to escape. Both tails and limbs can be regenerated. Adult frogs are unable to regrow limbs but tadpoles can do so. |
Amphibian | 621 | Anatomy and physiology | Amphibians have a juvenile stage and an adult stage, and the circulatory systems of the two are distinct. In the juvenile (or tadpole) stage, the circulation is similar to that of a fish; the two-chambered heart pumps the blood through the gills where it is oxygenated, and is spread around the body and back to the heart in a single loop. In the adult stage, amphibians (especially frogs) lose their gills and develop lungs. They have a heart that consists of a single ventricle and two atria. When the ventricle starts contracting, deoxygenated blood is pumped through the pulmonary artery to the lungs. Continued contraction then pumps oxygenated blood around the rest of the body. Mixing of the two bloodstreams is minimized by the anatomy of the chambers. |
Amphibian | 621 | Anatomy and physiology | The nervous system is basically the same as in other vertebrates, with a central brain, a spinal cord, and nerves throughout the body. The amphibian brain is relatively simple but broadly the same structurally as in reptiles, birds and mammals. Their brains are elongated, except in caecilians, and contain the usual motor and sensory areas of tetrapods. The pineal body, known to regulate sleep patterns in humans, is thought to produce the hormones involved in hibernation and aestivation in amphibians. |
Amphibian | 621 | Anatomy and physiology | Tadpoles retain the lateral line system of their ancestral fishes, but this is lost in terrestrial adult amphibians. Some caecilians possess electroreceptors that allow them to locate objects around them when submerged in water. The ears are well developed in frogs. There is no external ear, but the large circular eardrum lies on the surface of the head just behind the eye. This vibrates and sound is transmitted through a single bone, the stapes, to the inner ear. Only high-frequency sounds like mating calls are heard in this way, but low-frequency noises can be detected through another mechanism. There is a patch of specialized haircells, called papilla amphibiorum, in the inner ear capable of detecting deeper sounds. Another feature, unique to frogs and salamanders, is the columella-operculum complex adjoining the auditory capsule which is involved in the transmission of both airborne and seismic signals. The ears of salamanders and caecilians are less highly developed than those of frogs as they do not normally communicate with each other through the medium of sound. |
Amphibian | 621 | Anatomy and physiology | The eyes of tadpoles lack lids, but at metamorphosis, the cornea becomes more dome-shaped, the lens becomes flatter, and eyelids and associated glands and ducts develop. The adult eyes are an improvement on invertebrate eyes and were a first step in the development of more advanced vertebrate eyes. They allow colour vision and depth of focus. In the retinas are green rods, which are receptive to a wide range of wavelengths. |
Amphibian | 621 | Anatomy and physiology | Many amphibians catch their prey by flicking out an elongated tongue with a sticky tip and drawing it back into the mouth before seizing the item with their jaws. Some use inertial feeding to help them swallow the prey, repeatedly thrusting their head forward sharply causing the food to move backwards in their mouth by inertia. Most amphibians swallow their prey whole without much chewing so they possess voluminous stomachs. The short oesophagus is lined with cilia that help to move the food to the stomach and mucus produced by glands in the mouth and pharynx eases its passage. The enzyme chitinase produced in the stomach helps digest the chitinous cuticle of arthropod prey. |
Amphibian | 621 | Anatomy and physiology | Amphibians possess a pancreas, liver and gall bladder. The liver is usually large with two lobes. Its size is determined by its function as a glycogen and fat storage unit, and may change with the seasons as these reserves are built or used up. Adipose tissue is another important means of storing energy and this occurs in the abdomen (in internal structures called fat bodies), under the skin and, in some salamanders, in the tail. |
Amphibian | 621 | Anatomy and physiology | There are two kidneys located dorsally, near the roof of the body cavity. Their job is to filter the blood of metabolic waste and transport the urine via ureters to the urinary bladder where it is stored before being passed out periodically through the cloacal vent. Larvae and most aquatic adult amphibians excrete the nitrogen as ammonia in large quantities of dilute urine, while terrestrial species, with a greater need to conserve water, excrete the less toxic product urea. Some tree frogs with limited access to water excrete most of their metabolic waste as uric acid. |
Amphibian | 621 | Anatomy and physiology | Most aquatic and semi-aquatic amphibians have a membranous skin which allows them to absorb water directly through it. Some semi-aquatic animals also have similarly permeable bladder membrane. As a result, they tend to have high rates of urine production to offset this high water intake, and have urine which is low in dissolved salts. The urinary bladder assists such animals to retain salts. Some aquatic amphibian such as Xenopus do not reabsorb water, to prevent excessive water influx. For land-dwelling amphibians, dehydration results in reduced urine output. |
Amphibian | 621 | Anatomy and physiology | The lungs in amphibians are primitive compared to those of amniotes, possessing few internal septa and large alveoli, and consequently having a comparatively slow diffusion rate for oxygen entering the blood. Ventilation is accomplished by buccal pumping. Most amphibians, however, are able to exchange gases with the water or air via their skin. To enable sufficient cutaneous respiration, the surface of their highly vascularised skin must remain moist to allow the oxygen to diffuse at a sufficiently high rate. Because oxygen concentration in the water increases at both low temperatures and high flow rates, aquatic amphibians in these situations can rely primarily on cutaneous respiration, as in the Titicaca water frog and the hellbender salamander. In air, where oxygen is more concentrated, some small species can rely solely on cutaneous gas exchange, most famously the plethodontid salamanders, which have neither lungs nor gills. Many aquatic salamanders and all tadpoles have gills in their larval stage, with some (such as the axolotl) retaining gills as aquatic adults. |
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