CHAPTER IX 



A GENERAL REVIEW OF THE ANIMAL KINGDOM 



Before undertaking the study of the special groups into 

 which animals are arranged because of their apparent kinships, 

 it will be advantageous for the student to look briefly at the 

 whole field of animals, — the "animal kingdom." See Fig. 66. 



175. Class Mammalia. — Beginning with man himself it is 

 easy to see that there are numerous animals (as the apes and 

 monkeys; the various quadrupeds, as the horse, ox, dog, cat, 

 bears and squirrels; the whales and seals; and many others) 

 which differ much in general appearance from him but are like 

 him in very many remarkable particulars. For example, they 

 all (with certain exceptions) bring forth their youngalive and in 

 a more mature condition than is usual for other types of ani- 

 mals, the young being carried in a special organ of the mother's 

 body, often until development is well advanced. After birth 

 the mother produces milk in special glands for the nourishment 

 of the young to a still more mature stage. This is seen in no 

 other group of animals beside the mammals. The skin produces 

 hair or wool as a covering for the body. Man differs from the 

 other mammals in certain particulars but not nearly so much 

 as he and they differ from other animals. 



176. Class Aves. — Another well-developed but relatively 

 small group of animals is the class known as birds. There is 

 scarcely another class of animals so easy to distinguish at sight 

 as this. They equal or surpass the mammals in specialization, 

 but are very different from them. They are commonly recog- 

 nized by the body-covering of feathers, the modification of the 

 front limbs into wings for purposes of flight, and by the fact that 

 the jaws are sheathed in horny matter and, at least in present 

 day types, birds do not possess teeth. 



177. Class Reptilia. — This is a class recognized by zoologists 

 which is not nearly so easy to define or to identify as either of 



144 



