MAMMALIA 



441 



parts of course differ much and are to be connected with the 

 habits of life. Most of the Mammalia are quadrupeds (except 

 the allies of the whales, the porpoises, and the sea-cows); and 

 all except man, and some of apes most like him, have the axis 

 of the body in a horizontal position supported by all four 

 appendages, or by the medium. The aquatic types — whales, 

 porpoises, etc. — become more or less fish-like in form, in adapta- 



FiG. 233. 



Fig. 233. Diagram of Skin in Mammals, by Folsom. 



tion to the medium. There is an enormous range in size in 

 the group, — ^from the mice to elephants and whales. 



450. Supplementary Topics for Laboratory and Field Work. — Compare the 

 relative size, length, etc., of head, neck, trunk and tail of various types of mammals, 

 — using well known animals and the figures and descriptions of less familiar ones. 

 Can you find any signs of connection between any of these facts and known habits 

 of the animals studied? 



