386 ELEMENTARY ZOOLOGY. 



With all their differences the carnivores and the un- 

 gulates have many fundamental points in common. They 

 are all warm-blooded, covered with hair, have mammary 

 glands, carry the young in the uterus attached by a 

 placenta. Hence they belong to the sub-class placentals 

 and to the class of mammals. They have similar parts 

 to their skeletons, similar arrangements of the principal 

 muscles, similar structure of the brain and central nervous 

 system. Thus it might be shown that the newfoundland 

 and the spaniel are similar to all the vertebrates, and 

 finally to all the animals. 



If the similarities of structure in a litter of kittens is a 

 sign of kinship, we may equally believe that the simi- 

 larities between the dog and the cow are also evidences 

 of kinship; and that their differences mark a gradual 

 evolution from a common stock in special directions and 

 in adjustment to special modes of life through long 

 ages of time. 



384. Evidences from Rudimentary Organs. It often 

 happens that some animals possess organs in only a 

 slight or rudimentary way, which in other animals are 

 well developed and useful. In the rabbit, for example, 

 there is a pouch called the cecum at the junction of the 

 small and the large intestine. It is several inches in 

 length, well supplied with glands, and probably of con- 

 siderable value in digestion. In many mammals this 

 structure is much reduced, and in man it is only found 

 as a "vermiform appendix," which certainly has no 

 such value as it has in the rabbit, and is thought by 

 many physiologists to be a positive menace. 



Similarly, in many mammals, there are certain muscles 

 by which the external ear is moved and directed so as to 



