THE EVOLUTION OF MAN 



question whatever of any comparison between 

 the one or the other of these groups in the matter 

 of the flying apparatus. Each one of them, un- 

 der pressure of conditions, has separately ac- 

 quired this adaptation. A number of the old and 

 extinct saurians, such as the Dinosaurians, the 

 Pterodaktyls, or flying dragons, must have been 

 in possession of permanently warm blood, so far 

 as we are able to ascertain. A few snakes, such 

 as the python, develop to this day warm blood, 

 under certain conditions, for instance, when 

 they have laid eggs and wish to give them a cer- 

 tain amount of heat in hatching. So, it was na- 

 tural that the bird should acquire for life a cer- 

 tain faculty which appearel already among rep- 

 tiles from which it is descended. As we have 

 seen, the strange Archaeopteryx still represents 

 an unmistakable transition form from the general 

 reptile type to the bird. On the other hand, no 

 visible line leads from birds to mammals. The 

 bat is no more such a transition stage than a 

 whale is a transition from mammals to fish. In 

 both cases relatively highly developed mammals 

 have acquired independent adaptations, the bats 

 a flying apparatus and the whales a swimming 

 apparatus. 



It is not difficult to imagine that the feathers 



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