446 ZOOLOGY sect. 



CLASS VI.— MAMMALIA. 



The class Mammalia, the highest of the Vertebrata, comprises 

 the Monotremes and Marsupials, the Hoofed and Clawed Quadru- 

 peds, 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 through- 

 out life, lungs being, as in Reptiles and Birds, the sole organs of 

 respiration. The blood of Mammals has a high temperature, 

 resembling in that respect 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 

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

 form a thick, soft covering or fur. The young are nourished after 

 birth by the secretion of mammary or milk-glands. 



1. Example of the Class — The Rabbit [Leims mnimlus). 



Sxternal Characters. — The Rabbit (Fig. lOSO) is a four- 

 footed or quadrupedal animal, having the whole surface of its 



Fig. 1080,— lepus cuniculus. Jjateral view of skeleton with outline of body. 



body covered with soft fur. The head bears below its anterior 

 extremity the mouth, in the form of a tranverse slit bouuded by 

 soft lips. The upper lip is divided by a longitudinal cleft, running 

 backwards to the nostrils, and exposing the chisel-shaped incisor 

 teeth. Behind the incisor teeth the hairy integument projects on 

 each side into the cavity of the mouth. At the end of the snout, 

 above the mouth, are the nostrils, in the shape of two oblique slits. 

 The large eyes, situated at the sides of the head, have each three 

 eyelids, an upper and a lower hairy lid, and an anterior hairless third 

 eyelid or nictitating membrane, supported by a plate of cartilage. 

 Vibrissm— very long stiff hairs — are scattered above and below the 



