Evolution 



and 101 have forsaken their native element the one for the land, 

 the other for the water. 



The birds agree with the mammals in the development of a 

 four-chambered heart, in their warm blood, in their external 

 covering for the skin, and in the development of arrangements 

 and instincts for the parental care of the young. Their line of 

 Evolution has thus been to some extent parallel to that of the 

 mammals. On the other hand, they differ obviously in the structure 

 and function of their fore limbs, in the absence of a diaphragm, 

 and in their special methods for the care of the young, and there 

 can be no doubt that the two groups have had quite different 

 origins in the reptile class. 



120 



