192 ADAPTATION 



To be eifective the deviation must be pre- 

 served, but it is not necessary to enter into any 

 discussion of Natural Selection. This very occa- 

 sion bears evidence of the all but universal ac- 

 ceptance of the principle. It forms part of 

 nearly every theory of the origin of adaptation. 



B. The Material. In discussing the origin 

 of adaptations I shall confine myself mostly to 

 the brief examination of some of the adaptations 

 in the American Characins, to determine, if pos- 

 sible, to what extent different factors of evolu- 

 tion have contributed to their origin. 



The Characins are fresh-water fishes now in 

 their prime in tropical Africa and in tropical 

 America. 



I hope I need not apologize for confining my- 

 self to a bit of the wealth of that continent, 

 South America, which has been the training 

 ground of Darwin, Wallace, Bates, Miiller, and 

 so many of their supporters. 



In America there are known about six hun- 

 dred species ranging from the borders of the 

 United States to Patagonia. Different mem- 

 bers are adapted to nearly all possible fish envi- 

 ronments, both physical and biological. There 

 are mud-eaters without teeth, flesh-eaters Avith 

 teeth like a mowing-machine, and others with 

 long fang-Hke canines projecting through the 

 upper jaw when the mouth is closed. In the Es- 

 sequibo River I caught over forty species in one 

 day. Some of these minute translucent species 



