CHAPTER XXXI 

 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 squir- 

 rel serves to introduce the Mamma'lia, the highest class of 

 the animal kingdom. Mammals are warm-blooded verte- 

 brates 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 invariably present, in the majority of cases occurring 

 in two sets. 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 (OrnitJiorJiyn' chus 

 anati'nm, Fig. 215) 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 

 special characteristics. The name Monotrem'ata is given to 

 them in reference to the fact that these mammals possess but 

 a single opening (cloaca) through which the contents of the 

 intestine and the urinary and reproductive products pass 

 outward, as in the case of amphibians, birds, and reptiles. 

 Monotremes also stand alone among mammals in the fact 



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