5IO 



NATURE 



{Sept. 25, 1879 



tail, as I said, bears a relation to the region it in- 

 habits. For Brazil consists mainly of an enormously 

 extended forest, South America presenting us with the 

 main forest region of the world. Consequently, the 

 animals inhabiting this region must be fitted for an excep- 

 tionally arboreal life. The primeval forest exhibits as it 

 were a world borne aloft upon enormous pillars. 



Walking in such a forest, one wanders in obscurity 

 amongst enormous lofty trunks, at the summits of which 

 is a mass of entangled foliage high over head, and shutting 

 out almost completely the sun's rays from below. It is 

 in this upper world that most of the forest animals live, 

 and such conditions necessitate in them special modifica- 

 tions of structure, of one kind or another, and the pre- 

 hensile character of the kinkajou's tail is one such modifi- 

 cation. I do not mean to say that animals with prehensile 

 tails are not found elsewhere ; we shall shortly see that they 

 are. Neither do I mean to say that this particular cha- 

 racter is universal amongst forest-living beasts of South 

 America. The sloths, for example, are notoriously and 

 exclusively forest-dwellers, and they are most exception- 

 ally modified to suit their dwelling-place ; but the mode 

 of modification by which they are suited to a forest home 

 is of quite another kind ; it is one, however, which it would 

 be beside our purpose to enter upon to-day. Neverthe- 

 less, this particular character of tail does crop up amongst 

 South American beasts remarkably. Thus, for example, 

 let us consider the great order of monkeys. Monkeys are 

 scattered over almost all the warmest parts of the earth 

 save the West Indies, Madagascar, New Guinea, and 

 Australia. A great variety of species are found in Africa, 

 India, and the Indian Archipelago, and many of them have 

 long tails ; but not one kind of monkey in Asia or Africa 

 has a prehensile tail. In South America, however, we 

 find apes (such as the Howling Monkeys and the Spider 

 Monkeys) which have tails most perfectly prehensile, for 

 they are naked beneath towards the tip, and on that 

 account can be applied more closely and firmly to any 

 object grasped more firmly by the tail than they could be 

 grasped were the tail entirely hairy. The tail, indeed, is 

 not only capable of alone supporting the weight of the 

 body, but even of seizing a small movable object, and 

 bringing it in as a hand would do to the mouth. 



Monkeys may have long or they may have short tails, 

 and there are some which have no visible tails at all. 

 This is the case with the only European ape — the one 

 •which inhabits the Rock of Gibraltar. It is also the case 



to be seen, though none is visible in the unmutilated adult 

 body. In the earliest stages of our existence, however, 

 there is for a short time a real tail of considerable relative 

 extent, but in the development of the body it becomes 

 stationary, so as rapidly to become altogether overshadowed 

 and hidden. 



Fig. I. — Caudal vertebrae cf Ikuus. 



with the Gibbons, or long-armed apes (which we have had 

 living here from time to time, and some of which are so 

 remarkable for their powers of voice). It is also the 

 case with the orang-outang, the chimpanzee, and gorilla, 

 which are as devoid of tails as we are. But are they, and 

 are we, really devoid of tails ? Practically, of course, we 

 are so, but nevertheless the spinal column has a rudi- 

 mentary continuation formed of a few very imperfect 

 vertebrje— not sufficiently elongated to form an external 

 projection, so that in the human skeleton a minute tail is 



Fig. 2.— The Coccyx. At its upper end are the two prezygapophyses. 



As I have said, Madagascar is not inhabited by 

 monkeys, but it is inhabited, instead, by creatures called 

 lemurs, with long fox-like muzzles, of which several are 

 now living in our monkey-house. There also there was 

 lately living another Madagascar creature (a near ally of 

 the lemur) called Chierogaleus, and some of these creatures 

 are said to present an interesting peculiarity in the tail. 



Although Madagascar is a hot country, yet some of the 

 animals inhabiting it fall into a profound sleep, or torpor, 

 during the dry season, just as our own hedgehog falls into 

 a profound torpor during the winter. Now some of these 

 little lemur-like animals, called Cheirogalei, accumulate 

 during a part of the year a great quantity of fat in the 

 tail, which, in consequence, appears much swollen and 

 enlarged. Upon this fat the animals appear to subsist 

 during the other part of the year— not, of course, that 

 they eat it, but that it becomes gradually absorbed, so 

 that as the year comes round, the tail becomes as small 

 again as it was when the fattening process began. 



I have shown you how rudimentary the tail is in our- 

 selves. There are many other animals, however, in 

 which there is no tail. In certain bats the bones of the 

 tail are firmly united at their hinder end with the bones 

 of the hip-girdle or pelvis, so that at first sight there 

 seems to be even less tail in them than in ourselves. 



Very different is the condition of the tail in other bats, 

 such as in all those which fly about in summer evenings 

 in England. 



These creatures fly by means of wings which are hands 

 with fingers enormously long and exceedingly slender, 

 and tied together by skin, their hands being web-fingered 

 as a duck's foot is web-toed. But not only does this skin 

 extend between the long fingers, it also extends from the 

 hands to the sides of the body and legs, forming an enor- 

 mous membranous wing on each side of the body. 



The tail is similarly conditioned. A membrane extends 

 inwards from the whole length of the inside of each leg, 

 and joins the adjacent side of the tail, which is thus- 

 held in a membrane called inter-femoral, from its situa- 

 tion. In the bat the tail serves as a rudder in flying, but 

 it also performs another function, for by the bending for- 

 wards of the tail and the inter-femoral membrane it serves 

 as a cradle in which the infant bat is held on its first 

 appearance in the world. 



An "inter-femoral membrane" extending from the legs 

 to the tail between them, also exists in an animal of a 

 widely diiiferent form and nature, namely, in the seal. 



The two hind legs of the seal are of no use whatever 

 to the animal for progression on land, and the seal thus 

 dififers from the sea-bear. The hind-legs of the seal are- 

 kept extended out backwards, much in the position in 

 which a man holds his legs when he swims. But they 

 act in quite a different way in swimming from the way 

 our legs act. Being united by an inter- femoral membrane 

 with the tail, the whole mass of the legs and tail together 

 form a sort of fin, which strikes the water as a whole, 

 and so propels the body of the animal along in the 

 water. . 



Very different is the tail of the whale, porpoise, or such 

 a creature as the manatee or the dugong. None of these 

 creatures have hind-legs at all, or but the merest rudiment 



