ADAPTATION 201 



phants, etc. Indeed, one may speak with propriety of a 

 Puerco, or Wasatch, or White River type of skull, which 

 wiU be found exemplified in widely separate orders." 



One adaptation has not arisen once but many 

 times/ To repeat, "Adaptations arise when- 

 ever needed, if they are at all possible." 



4. Origin of geographical and geological di- 

 vergence and convergence. All these facts tend 

 to show that adaptations have arisen as the result 

 of the peculiarity of the environment. How? 



It has been demonstrated many times that the 

 individual is modified by his physical environ- 

 ment. It is claimed on the one hand that the 

 deviation is maintained by its transmission to the 

 germ-plasm, and thus the next generation; and, 

 on the other, that the environment, in some cases 

 at least, directly affects the germ-plasm. 



There is a third possibility. In some localities 

 the individuals of certain species are very dark, 

 in others they are practically without color. If 

 the latter individuals are examined closely it is 

 found that they are abundantly supplied with 

 chromatophores, and only the needed environ- 

 mental stimulus is lacking to bring out the strong 

 color. This is not a matter of the simple expan- 

 sion or contraction of the pigment, which may 

 take place in a few moments, but the develop- 



* Among characters that have appeared several times inde- 

 pendently in the Characins may be mentioned: The incomplete 

 lateral line, the scaled caudal, three series of teeth in the pre- 

 maxillary, a pair of canines in the lower jaw, ctenoid scales, 

 incisor-lUte teeth. 



