494 ZOOLOGY 



whether a special quaUty that is gained by the body cells in 

 their life can be imparted to their cousins among the germ cells 

 from which the next generation of individuals arises. Unless 

 this can be done it is clear that these bodily changes cannot be 

 transmitted to the next generation, since the body cells do not 

 themselves pass over. A body may have acquired a very strik- 

 ing quality, as a mutilation for example, without any part of 

 this quality being found in the germ cells and thus being 

 preserved. 



B. Preservation of changes that come to the substance of the 

 germ cells. Clearly, since the germ cells make the next genera- 

 tion, changes in these cells may very well influence both the germ 

 and body cells of the next generation, and no new quality can 

 be passed on to the next generation without somehow first 

 becoming represented in the germ plasm. Biologists are coming 

 more and more to feel that this is the really great field of heredi- 

 tary influence, and that evolutionary studies must concern 

 themselves increasingly with the history of these cells and the 

 kinds of influences that can change them. 



3 . The Guidance of Evolution. — Whether we believe that the 

 course of evolution has been purposive or not, we can, as we 

 look back upon the course of it, see that it has actually pro- 

 ceeded toward certain reasonably definite goals. If evolution 

 has been in any degree orderly, there must have been some 

 guiding influences. Variations may themselves occur in an 

 orderly or guided fashion, or if they are haphazard there must 

 have been something which has guided in their preservation. 

 This might take place in either, or both, of two ways. 



a. If variation is guided so that chiefly suitable or appro- 

 priate changes shall occur, evolution would be controlled 

 thereby. It is conceivable that organisms have an internal 

 tendency to vary in definite and suitable directions; or that 

 the environment naturally forces the changes in organic matter 

 into channels that are fit. 



b. Or, on the contrary, variations may have any range, and 

 the environment through its life and death pressure on the 

 organisms may eliminate some and select others on the basis of 

 the fitness of their variation. The result of this would be to 



