122 ZOOLOGICAL PHILOSOPHY 



Thus in the pachyderms, some have five digits on their feet invested 

 in horn, and their hoof is consequently divided into five parts ; others 

 have only four, and others again not more than three ; but in the 

 ruminants, which are apparently the oldest of the mammals that are 

 permanently confined to the ground, there are not more than two 

 digits on the feet and indeed, in the solipeds, there is only one (horse, 

 donkey). 



Nevertheless some of these herbivorous animals, especially the 

 ruminants, are incessantly exposed to the attacks of carnivorous 

 animals in the desert countries that they inhabit, and they can only 

 find safety in headlong flight. Necessity has in these cases forced 

 them to exert themselves in swift running, and from this habit their 

 body has become more slender and their legs much finer ; instances 

 are furnished by the antelopes, gazelles, etc. 



In our own climates, there are other dangers, such as those con- 

 stituted by man, with his continual pursuit of red deer, roe deer and 

 fallow deer ; this has reduced them to the same necessity, has impelled 

 them into similar habits, and had corresponding effects. 



Since ruminants can only use their feet for support, and have little 

 strength in their jaws, which only obtain exercise by cutting and 

 browsing on the grass, they can only fight by blows with their heads, 

 attacking one another with their crowns. 



In the frequent fits of anger to which the males especially are subject, 

 the efforts of their inner feeling cause the fluids to flow more strongly 

 towards that part of their head ; in some there is hence deposited 

 a secretion of horny matter, and in others of bony matter mixed with 

 horny matter, which gives rise to solid protuberances : thus we have 

 the origin of horns and antlers, with which the head of most of these 

 animals is armed. 



It is interesting to observe the result of habit in the peculiar shape 

 and size of the giraffe (Camelo-pardalis) : this animal, the largest of 

 the mammals, is known to live in the interior of Africa in places where 

 the soil is nearly always arid and barren, so that it is obliged to browse 

 on the leaves of trees and to make constant efforts to reach them. 

 From this habit long maintained in all its race, it has resulted that 

 the animal's fore-legs have become longer than its hind legs, and that 

 its neck is lengthened to such a degree that the giraffe, without standing 

 up on its hind legs, attains a height of six metres (nearly 20 feet). 



Among birds, ostriches, which have no power of flight and are raised 

 on very long legs, probably owe their singular shape to analogous 

 circumstances. 



The effect of habit is quite as remarkable in the carnivorous mammals 

 as in the herbivores ; but it exhibits results of a different kind. 



