CLASSIFICATION 17 



intelligence to be likened to man, and we forget that 

 it is their having intelligence at all which justifies us 

 in regarding them as fundamentally related to him. 



From the apes we may pass to all the remaining 

 animals that suckle their young and are coated with 

 hair. These — the Mammalia — are interconnected by 

 ties of structural agreement which investigation dis- 

 covers in almost every bone and tissue, and even in 

 the very blood itself. As proof of relationship, blood has 

 lately vindicated its claim to pre-eminence. There is a 

 test to which the blood of each mammal responds, and 

 the nature of this response given by one species, 

 compared with that of any other species, shows the 

 close or remote connection between the two animals. 



Ranking below the hairy animals, those of feather 

 and scale flock together. Unlike as birds and reptiles 

 seem, the connection between them is closer than 

 that between either and any known third group of 

 animals. It is seen in the construction of the bony 

 framework, of the muscles and tendons, in the 

 blood and in the eye, in the brain and in the egg. 

 All the differences which exalt the bird — warmth and 

 sustained activity, voice and exuberance — are the 

 outcome of reptilian characters. 



After the reptiles come the sluggish Amphibia, 

 creatures of the swamps — the newts, salamanders, 

 frogs, and toads. Breathing both through the skin 

 and by the lungs, these animals arc only partially 

 emancipated from aquatic life. In this and other 

 respects they stand halfway between reptiles and fish. 



