CLASS MAMMALS. 



349 



343. Relations to Man. The group is of especial 

 theoretical interest to us, because it is the class to which 

 we belong. It is furthermore the class of animals on 

 which we are most dependent for the comforts of life. 

 They furnish our beasts of burden, the bulk of our flesh 

 foods, many of the materials for our clothing, beside a 

 great number of miscellaneous articles commonly used 

 by civilized peoples. Man doubtless could live on the 

 earth without the aid of the mammals, but life would 

 be a very different thing from what it is at present. If 

 mammals have influenced man, he has even more pro- 

 foundly influenced them. The great carnivorous animals 

 that have been most unfriendly to man are gradually 

 but surely disappearing before him. The greatest change 

 which man has wrought, however, upon the class is through 

 the domestication of those species which were at once 

 useful and easy of domestication. 



344. Practical Exercise. The student should enumerate as many 

 as possible of the materials used by man which have a mammalian 

 origin, and determine the exact source of each. Where do the 

 mammals live which supply these various materials? 



345. Leading Types of Mammals. Reference has already been 

 made to the division of the group into three sub-classes tnonotremes, 

 marsupials, and placentals. The monotremes include only a few 

 forms confined to Australia and the neighboring islands. The 

 Duck-mole (Fig. 148) is one of these. 



The marsupials are more numerous and comprise the native 

 mammalian fauna of Australia. The kangaroo, a vegetable feeder, 

 is the largest and best known of these, but there are numerous 

 others with habits varying all the way from those of the rodents to 

 the carnivorous life of cats and bears. The only native marsupial 

 we have is the Virginia opossum (Fig. 149) . Other species are found 

 in South America. The marsupials are the mammals of a former 

 geological age, and those on the earth now are to be looked upon as 

 remnants rather than as a real branch of the modern mammals. 



The following orders all belong to the placentals or true mammals. 



