192 



EVOLUTION 



The bisoD, an almost extinct mammal. 



Adaptations in Mammalia. — Of the thirty-five hundred species, 

 most inhabit continents; a few species are found on different islands, 

 and some, as the whale, inhabit the ocean. They vary in size from 

 the whale and the elephant to tiny shrew mice and moles. Adapta- 

 tions to different habitat 

 and methods of life abound ; 

 the seal and whale have 

 the limbs modified into 

 flippers, the sloth and 

 squirrel have limbs pecul- 

 iarly adapted to climbing, 

 while the bats have the 

 fore limbs modeled for 

 flight. 



Lowest Mammals. — The 

 lowest are the monotremes, 

 animals which lay eggs like 

 the birds, although they are 

 provided with hairy covering like other mammals. Such are the Aus- 

 tralian spiny anteater and the duck mole. 



All other mammals bring forth their j^oung developed to a form simi- 

 lar to their own. The kangaroo and opossum, however, are provided 

 with a pouch on the under side of the body in which the very immature, 

 blind, and helpless young are nourished until they are able to care for 

 themselves. These pouched animals are called marsupials. 

 The other mammals may be briefly classified as follows : — 



Classification of Higher Mammals 



Order I. Edentata. Toothless or with very simple teeth. Examples: anteater, 

 sloth, armadillo. 



Order II. Rodentia. Incisor teeth chisel-shaped, usually two above and two 

 below. Examples : beaver, rat, porcupine, rabbit, squirrel. 



Order III. Cetacea. Adapted to marine life. Examples : whale, porpoise. 



Order IV. Ungulata. Hoofs, teeth adapted for grinding. Examples : (a) odd- 

 toed, horse, rhinoceros, tapir ; (6) even-toed, ox, pig, sheep, deer. 



Order V. Carnivora. Long canine teeth, sharp and long claws. Examples : dog, 

 cat, lion, bear, seal, and sea lion. 



Order VI. Insectivora. Example : mole. 



Order VII. Cheiroptera. Fore limbs adapted to flight, teeth pointed. Example: bat. 



Order VIII. Primates. Erect or nearly so, fore appendage provided with hand. 

 Examples : monkey, ape, man. 



