

PHYLUM CHORDATA 



417 



i-s, thr Piearise, and especially the Passeres. Among the latter 

 Yrvi1;i- (Crows) are probably to be looked upon as the most 

 ubers of the class (Fig. 1016 bis). 



PASSERES 



GAVIAE 

 COLYMBI \ICHTHYORNITHES 



OOONT 



GALLINAE 



CRYPTURI 



MEGISTANES 



ARCHAEORNITHES 



ORNITHOSAURIA 



OINOSAURIA 



FIG. 1016645. Diagram illustrating the Relationships of the chief groups of Birds. 



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. EXAMPLI OF THE CLASS THE RABBIT (LepUS CUUlCulus). 



External Characters. The Rabbit (Fig. 1017) is a four- 

 footed or quadrupedal animal, having the whole surface of its 



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