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THE USES OF TAILS IN ANIMALS.

A general meeting of the National History and Microscopical Society was held on Monday night, at the Midland Institute; Mr. A. W. Mills presiding. A paper was read by the PRESIDENT, prepared by Mr. Lawson Tait, on "The Uses of Tails in Animals." He said it was not difficult to imagine how the prehensile tails of monkeys, opossums, and other animals, or the fly-switches of the horse or cow, have been useful in the struggles of these animals to master their surroundings; but there are some forms of the appendage which puzzled them to see how they can ever have been available as assistants in survival, and still more how they are still perpetuated in their apparently purposeless forms. Amongst them the bushy tail seen in the fox, dog, cat, &c., had long attracted his attention, and no intelligible meaning of it suggested itself to untill he came into possession of a cat which is perfectly deaf, and on whom he could therefore perform many experiments which would be impossible in an animal possessed of hearing. Like all cats, he was very fond of a warm place, and when he was asleep nothing but a touch or a very strong vibration communicated through what he is lying upon would wake him. If he went to sleep before a big fire, he slept lying on his side, at full length, with head, tail, and limbs all stretched out. But if screens were placed between him and the heat, he gradually coiled himself up, apparently without waking, covering his limbs with his tail and head, so that as little surface was exposed as possible for loss of heat. If, in addition to screening off the heat, a direct current of cold air was directed on him by means of a bellows, he soon buried his nose in the fur of his tail, or between his tail and thigh, so that almost his whole face is protected. On the heat being readmitted the whole movements were reversed, and he resumed his extended position. The use of the tail was clearly, therefore, completely analogous to that of the respirator worn by people with delicate chests, the object being to extract from the expired air, by means of fur in the one case and wire gauze in the other, the heat which was being taken out with it; so that the cold inspired air shall be raised in temperature before it reached the lungs, and thereby conduce to a conservation of the bodily heat. Some interesting considerations bear on this. Animals provided with bushy tails seemed to be so as a matter of correlation of growth, their bodies were always provided with thickly set and more or less soft fur. He (Mr. Tait) could not find an animal with a bushy tail which could not, and did not, lie curled up when asleep. He went round the Zoological Gardens at Dublin on a very cold morning in February, in company with Professor Haughton, and they the civet cat, and some other bushy-tailed animals, coiled up with their noses buried in the fur of their tails. In the squirrel this use of the tail is very marked and in birds the same object is accomplished by their burying their heads in the down of their shoulders. Animals provided with bushy tails, so far as he could find, were all solitary in their method of living and, therefore one essential for their survival was some method by which variations of temperature should be resisted. The use of the tail for this purpose was, he thought, best of all illustrated in the great ant-eater (myrmecophaga jubata), in which the hairs of the tail reach a very great size, and covered up the animal when reposing, so that he looked like a bundle of dried grass. It might also serve as a protection by mimicry in this case. Mr. Wallace stated,¹ also, that he used his tail as an umbrella in a shower, and that the Indians diverted its attention from themselves by rustling the leaves in imitation of a falling shower, and while he is putting up his umbrella they killed him. Some of the myrmecophaga have the lower end of the tail naked, and used it as a prehensile organ, whilst the upper part remained covered with long hair, and is used as a respirator. In other edentulous animals, living in tropical countries where they are not subjected to extremes of temperature, the long hairs were replaced by scales, as in the pangolins, or the tail was absent, as in the sloth. Among the rodents two very curious contrasts in the matter of tail are presented by the guinea-pig and the squirrel. The former was gregarious, and any one who had kept a hutch of guinea-pigs must have seen how they protected themselves from loss of heat by packing themselves in rows arranged heads and tails; whilst the squirrel was solitary and in his nest, during his winter sleep, coiled himself up and covered his face with his tail. The same is seen in the dormouse, and in the gerba during hibernation. Of the Carnivora, those which had bushy tails were all solitary in their method of living, though the wolf and jackal hunted in packs, and those with the bushiest tails were most exposed to low temperatures, as the Arctic fox and sable. Of the Quadrumana, the marmorets afforded a striking instance of a bushy tail as a probable provision for protecting these delicate creatures from depression of their temperature. He had received an interesting letter² from Mr. Darwin on this point, in which he said, "Your view is new to me, and has only to be suggested for its probability to be recognized. I presume that of course you would thus account only in part for the retention of a tail, and for its modification. Your view does not preclude the conjoint use of the tail for other service, as for gliding through the air when flattened, as in the squirrel, or as a signal to beasts of prey, in accordance with Mr. Belt's ingenious suggestion in his 'Nicaraguan Travels,'³ with respect to the great bushy and conspicuously-coloured tail of the skunks. I wish we knew the use of the extraordinary hairy tail of the yak, which inhabits such cold regions, whether it serves solely as a fly-flapper. If poor Dr. Falconer⁴ had been alive, he could have told us." In reply, he (Mr. Tait) said that he had missed the yak in his search for animals with bushy tails, but he found that the yak also had a long abdominal fringe of hair nearly touching the ground. When the animal lay down with his limbs drawn up to, or under him, as all ruminants did, his tail and fringe would act as a rug, preventing loss of heat from the limbs and damage to them from frost-bite, as the tissues outside the bone were thin, and there was nothing but a rather weak circulation to resist loss of heat. The yak lived close to the line of perpetual snow, which was the condition in which such epithelial appendages as he had would most conduce to survival, and therefore that in which they would be most easily evolved by natural selection. This seemed to point out a curious study of the mechanical arrangements which existed in animals for the conservation of heat—a very important element in the struggle for life. Some forms of tails were yet a puzzle to him—notably the tails of rats and mice, for which he had as yet found no reasonable explanation.

¹ Alfred Russel Wallace. Wallace 1853, p. 452: "During rain it turns its long bushy tail up over its back and stands still; the Indians, when they meet with one, rustle the leaves, and it thinks rain is falling, and turning up its tail, they take the opportunity of killing it by a blow on the head with a stick."

² Darwin wrote this letter 13-15 March 1875 in response to a letter of 12 March [1875] by Lawson Tait [born Robert Lawson Tait] (1845-1899) Birmingham surgeon, gynaecologist and anti-vivisectionist. On 16 March [1875] Tait wrote to thank Darwin for his reply. See Correspondence vol. 23. Much further information on the connections between Lawson Tait and Darwin can be found by searching the texts in Darwin Online, here. See also the printed items in Darwin's papers by Lawson Tait here.

³ Belt 1874. In CUL-DAR88.94 Darwin noted "Belt p 250 Skunk signal of Danger — Tail". In Descent 2s ed., p. 543, Darwin wrote:

Colour seems to be advantageous to another animal, the skunk, in a manner of which we have had many instances in other classes. No animal will voluntarily attack one of these creatures on account of the dreadful odour which it emits when irritated; but during the dusk it would not easily be recognised and might be attacked by a beast of prey. Hence it is, as Mr. Belt believes, that the skunk is provided with a great white bushy tail, which serves as a conspicuous warning.

Darwin seems never to have written on the evolutionary origins of yak tails, though he did remark, in Variation 2: 206 "According to Pallas the Mongolians endeavour to breed the Yaks or horse-tailed buffaloes with white tails, for these are sold to the Chinese mandarins as fly-flappers".

⁴ Hugh Falconer (1808-1865), physician and palaeontologist.