Sept. 25, 1879] 



NATURE 



511 



of such in the shape of a few very small bones buried in 

 the flesh. On the other hand, the tail is enormous in bulk, 

 and expands outwards on each side at its hinder end, 



but in this expansion there are no limb-bones whatevet ; 

 it is only a cutaneous expansion. This expansion extends 

 horizontaUy in these animals. Why is this ? 



Fig. 3.— Dugong. 



Fishes, such as the cod, perch, salmon, shark, &c., have 

 the ends of their tails expanded vertically, not horizon- 

 tally, and it is very evident why. 



Fishes swim by bending the tail from side to side and 

 striking the water laterally, as those in any aquarium will 

 show us. They also breathe by the water which flows 

 over their gills. 



Whales and porpoises arc not fishes, but they are (as 

 is also the manatee and the dugong) aquatic beasts, and 

 they breathe air by lungs as other beasts do. This is the 

 key to the difference in their tails, that is, the horizontal 

 expansion of the hinder end. They require to bring their 

 heads pretty often to the surface to breathe, and the 

 horizontally expanded tail is well fitted to help them in so 

 ascending by its downward blows. 



But the tail of the whale or porpoise, strange to say, 

 affords perhaps a partial explanation of the form of the 

 head in these animals. For whales and porpoises are 

 quite remarkable for the large size of their brains. Now 

 the brain is commonly supposed — and in many cases 



with much reason — to be related to the powers of sensa- 

 tion and imagination which animals possess. Yet it is 

 impossible to think that these marine creatures have any 

 need for exceptionally acute or powerful minds. 



But brain stuff is known to be related to motion, no 

 less than to feeling and imagination. Unless our muscles 

 were duly stimulated by nerves and by the brain and 

 spinal cord, they would not act. It may well be then that 

 these animals need all their brains to supply enough 

 nerrous energy for the incessant muscular exertion which 

 their habit of life renders necessary in the medium they 

 inhabit. But this explanation alone will not do, for fishes 

 have very small brains. The difference is perhaps due to 

 the fact that whales and porpoises need to maintain a 

 high body temperature, while fishes are cold-blooded and 

 brain stuff is needed to maintain bodily heat no less than 

 for sensation and motion. 



The tails of beasts are generally like their bodies, 

 covered with hair. The rat and mouse and certain opos- 

 sums offer exceptions in their naked, scaly looking tails. 



Fic. 4.— The Pangolin (Manh). 



One animal from Africa, a creature much like a fly- 

 ing squirrel {Anomalunis) presents (as its name implies) 

 a very exceptional condition of tail. It is really scaly in 

 part, for underneath it, at a little distance from its root, it 

 is furnished with horny overlapping scales. Such scales 

 are yet more developed in another beast — the manis or 

 pangohn— but then in this latter animal the whole body 

 and limbs are thus invested and not part of the tail only. 



The animal renowned for its curious naked tail — 

 flattened out like a trowel— is the beaver. As to the use 

 of this animal' s tail our experienced superintendent, Mr. 

 Bartlett (who is so acute and accurate an observer of 

 animals' habits) assures me that he has often watched 

 beavers when at work building with mud in snow, but in 

 no instance has he seen them make use of the tail as a 

 trowel as has so often been alleged. But the beaver 

 has great power in its tail, not only as an organ used in 

 swimming but as a means of sounding an alarm to its 

 comrades. On the approach of an enemy the beaver 

 strikes the surface of the water with its flat tail with such 

 force that it can be heard, on a still night, half a mile off. 

 Upon hearing this signal all the beavers in the neigh- 

 bourhood quickly dive under the water. 



The beavers which still linger in European rivers have 

 now ceased to construct dams as do their American 



fellows. It is an interesting fact, however, that they still 

 retained this habit in Europe down to the time of Albertus 

 Magnus, who of course knew nothing of the habits of the 

 beavers of the then undiscovered America. 



In the Zoological Gardens are creatures which are pro- 

 vided with exceptionally powerful tails — for land animals — 

 I mean the kangaroos. These creatures make use of their 

 tails not only sometimes to carry grass, and to a certain 

 extent in their long jumps, but constantly when sitting with 

 the fore part of the body raised, and in this position they 

 often raise themselves high up on their extended hind 

 legs and on their tail as on a strong tripod, at which time 

 they have a most comic appearance. 



And this brings me to speak of another matter. As I 

 have said the sloths are fitted to live in trees not by any 

 peculiar development of tail, but in other ways. Certain 

 gigantic extinct allies of sloths, however, were fitted for a 

 forest life and to live entirely on the foliage of trees by 

 their taih. Such extinct beasts were the Myloiion and 

 Megatherium, creatures equalling or exceeding the rhino- 

 ceros in bulk. 



The modification of tail specially adapted for forest 

 life with which we have as yet met, has been a prehensile 

 tail. This we have seen in the kinkajou and in howl- 

 ing and spider monkeys. Many other beasts, how- 



