Xii PHYLUM CHORD ATA 491 



bate, the eggs until the young are hatched, but in the Aus- 

 tralian mound-makers (Megapodius) the eggs are buried in 

 heaps of decaying vegetable matter, the decomposition of 

 which generates the necessary heat. 



/<fr CLASS VI. MAMMALIA 



The class Mammalia, the highest of the Vertebrata, com- 

 prises the Monotremes and Marsupials, the hoofed and 

 clawed quadrupeds, the whales and porpoises and sea-cows, 

 the rodents, bats, and insectivores, the lemurs and apes, and 

 the human species. All mammals, though many are aquatic, 

 are air-breathers throughout life, lungs being, as in reptiles 

 and birds, the sole organs of respiration. The blood of 

 mammals has a high temperature, resembling in that re- 

 spect the blood of birds, and differing from that of reptiles 

 and amphibia. The scales of reptiles and the feathers of 

 birds are replaced in mammals by peculiar epidermal struc- 

 tures, the hairs, usually developed in such quantities as to 

 form a thick soft covering or fur. 



The rabbit (Lcpus atiiiculus) will serve as a convenient 

 example of the class. 1 



The rabbit (Fig. 297) is a four-footed or quadrupedal ani- 

 mal, having the whole surface of its body covered with soft 

 fur. The head bears below its anterior extremity the mouth 

 in the form of a transverse slit bounded by soft lips. The 

 upper lip is divided by a longitudinal cleft, running back- 

 wards to the nostrils and exposing the chisel -shaped incisor 

 teeth. Behind the incisor teeth the hairy integument pro- 

 jects on each side into the cavity of the mouth. At the end 

 of the snout, above the mouth, are the nostrils in the shape 



1 The following account will apply in all but very slight details to our 

 cotton-tail rabbit or to our American hare. 



