86 THE PROBLEMS OF EVOLUTION 



source of the influence, chromosomes of one or the 

 other generation have much to do with the promor- 

 phology of the egg, for its immediate environment 

 is the maternal body. 



Promorphology goes far to establish the im- 

 portance of the cytoplasm in the cells of the body. 

 Since the cytoplasmic materials are variously dis- 

 tributed, they are apparently distinctive in the 

 various types of cells, at least in potentiality. 

 Associated with the complete chromosome com- 

 plex of the nucleus it is quite logical to expect 

 different results from the different cytoplasmic 

 materials. Were there no essential difference in the 

 cytoplasm of specialized cells, we might expect 

 them to undergo complete dedifferentiation when 

 removed from their normal environments; that 

 this is not the case is shown by tissue cultures, 

 where distinctive functional characteristics, at 

 least, are retained by the specialized cells and their 

 descendants. Even though the chromosome com- 

 plex is apparently complete in the various kinds 

 and the environment is uniform, the cells do not 

 assume a uniform character; this failure can only 

 be associated with their cytoplasmic differences. 



It is a strangely baffling situation, out of which 

 we can safely draw only meager conclusions, viz., 

 (1) that the chromatin of the cell is preeminently 

 a center of control which is dependent upon the 

 cytoplasm for its continued existence, but which 



