A LESSON !N COMPARATIVE ZOOLOGY. 409 



How shall we compare them, in order to find feature common to any two or 

 more of them ? 



Perhaps the feature that strikes us first would be the horns in the ox and the 

 deer. Can we associate these with any of the others ? 



If we examine the teeth of all the animals in the first, second and third lines, 

 except the elephant, we shall find them sharp and cutting, with long canine or 

 prehensile teeth, admirably adapted for seizing and holding living prey, and for 

 cutting and tearing it. We should, therefore, call these animals carnivorous. If 

 we examined the teeth of the animals in the fourth and fifth lines, we shall see 

 that they have large flat surfaces well adapted to chewing and grinding, and as 

 they live on vegetable substances, we shall call these animals herbivorous. 



Comparing still further, we find that in the horse and the ox, both herbivorae, 

 the horse has incisor teeth in the upper and the lower jaw, while in the ox there 

 are incisors in the lower jaw only, and this arrangement of teeth has a direct re- 

 lation to the different structures of the stomach in the two animals, the ox hav- 

 ing a complicated stomach with four pouches adapted to a mode of digestion by 

 which the food is prepared for a second mode of mastication. This order of 

 animals, those in the fourth line, are called ruminants. 



The animals in the fifth line have simple stomachs, and do not ruminate. 



If we again, compare the ox, this time with the deer, we shall find that while 

 both are herbivorous ruminants, and both have horns, in the ox the horn is hol- 

 low and remains firmly attached to the animal's head through life; in the deer it 

 is solid and is shed every year. 



Upon looking further we find that the pig, tapir and peccary, carnivorous 

 animals, have a cloven foot like the herbivorous animals in the fourth line, and 

 those last again, are different from the herbivorous animals in the fifth line, which 

 have a solid hoof or foot. 



These comparative studies will enable us to classify animals into different 

 orders and species. 



Naturalists tell us that certain animals sprang from a common stock, and the 

 differences between them are the results of modifications of structure gradually 

 occurring during long periods of time. Thus the pig has a stout rounded body 

 and a mobile nose. The peccary is a step higher. Then in the tapir, the body 

 is about the same, but the nose is decidedly more developed. The rhinoceros 

 comes in next with the same form of body, and his nose modified and turned up- 

 ward into one or two horns, and lastly the elephant, with his long mobile nose or 

 trunk, is the highest expression of this common stock. 



The order Felidse, or cats, are almost precisely alike, the differences being 

 chiefly of size, color, and growth of hair. The lion, tiger, panther, leopard, 

 puma, and cat certainly sprang from a common stock, the domestic cat, per- 

 haps, having the highest development, from the fact of its ability to rotate the 

 radius upon the ulna, a motion the larger cats do not have. We see the grace of 

 this motion when our cats play with a mouse or a ball of yarn. 



