64 



THE PRESENT. 



sified in structure, come the Vertebrata the fishes, reptiles, 

 birds, and mammals the inhabitants of every element, 

 and the tenants of every region, though culminating chiefly 

 in numbers and rank within temperate and warm parallels. 



Vertebrate Aspect of Animal Life. 



In general terms, the ascent in the zoological scale is from 

 the aquatic to the terrestrial, from the cold-blooded water- 

 breathers to the cold-blooded air-breathers, and from these 

 to the still higher warm-blooded air-breathers. The great 

 majority of invertebrate forms are confined to the w r aters : 

 a large proportion of the vertebrates are strictly terrestrial, 

 or own an amphibious existence. Between them and the 

 higher forms of terrestrial vegetation, the interdependence 

 is complete ; the existence of the higher flora being unin- 

 telligible in the absence of a higher fauna. The grasses, 



