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 Mammals. 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 bring 

 forth their young alive and in a more mature condition than 

 is usual for other types of animals, the young being carried 

 in a special organ of the mother's body, often until develop- 

 ment 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 Birds. Another well-developed and numerous 

 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 especially to be recognized 

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

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

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

 birds do not possess teeth. 



177. Class Reptiles. This is a class recognized by zoologists 

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



142 



