CHAPTER XXXIII 

 MAMMALS 



Vocabulary 



Ruminant, animals adapted for re-chewing their food. 

 Vertical, straight up and down. 

 Quadrupeds, four-footed animals. 



The mammals constitute the highest group of the animal kingdom 

 because in them the development of the brain, intelligence, and 

 reason have reached the highest degree of specialization. 



The birds excelled in adaptations for flight and in marvelous 

 instincts for nest-building and migration. The communal insects 

 have carried division of labor to a remarkable perfection, but if 

 we compare the real intelligence of these forms with that displayed 

 by a dog, a beaver, or a horse, not to mention man, we can see 

 that there is no question as to the mammal's position at the top. 



Mammals include man, the apes, quadrupeds, bats, seals, whales, 

 etc., and are a very diverse group as the tabulation shows. They 

 vary in size from the tiny harvest mouse that can climb a wheat 

 stem, to the enormous whale, a hundred feet in length. They are 

 found in all parts of the world except on a few small Pacific islands 

 and are the group of animals with which man (himself a mammal) 

 has had most to do. 



The chief characteristics of this important class are as follows: 



1. The young are born alive (no external eggs). 



2. The young are nourished with milk. 



3. The body is more or less covered with hair. 



4. The cerebrum is highly developed. 



5. A diaphragm (breathing muscle) is present. 



6. They have two sets of teeth and fleshy lips. 



7. High circulatory development, left aorta only. 



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