CHAPTER XXXVII 



THE ALLIES OF THE SQUIRREL: MAMMALIA 



They say, 

 The solid earth whereon we tread 



In tracts of fluent heat began, 



And grew to seeming-random forms, 

 The seeming prey of cyclic storms, 



Till at the last arose the man. 



Tennyson, In Memoriam 



Definition of Mammalia (Lat. mamma, "breast"). The 

 squirrel serves to introduce the Mammalia, the highest class 

 of the animal kingdom. Man himself belongs to this class. 

 Therefore all facts of structure and of function mentioned 

 in the preceding chapter have especial interest for us. All 

 mammals are much alike in their anatomy and physiology. 



Mammals are warm-blooded vertebrates covered with 

 hair. Generally two pairs of appendages are present, the 

 anterior of which are never absent in any member of the 

 class. Mammals breathe by lungs. Teeth are almost in- 

 variably present. In the majority of cases the "milk teeth ,: 

 of the young are shed and an entirely new set develops in 

 the adult. Mammals bring forth their young alive and feed 

 them on milk, except in the very few cases to be referred to 

 under the Monotremata below. 



The principal orders into which the class is divided are 

 mentioned in the following pages. 



The Duckbill and Allies. The duckbill (Ornithorhyn'chus 

 anati'nus, Fig. 216) and two or three species of spiny ant- 

 eater (Echid'na), mammals of the size of a rabbit and found 

 only in Australia, Tasmania, and New Guinea, have many 



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