104 THE PROBLEMS OF EVOLUTION 



the domestic fowl the male germ cells arising after 

 the destruction of the ovary are formed from the 

 peritoneal epithelium, both of the degenerating 

 ovary and of the vestigial right ovary. More con- 

 vincing evidence that the genes in somatic cells 

 may retain their full powers could not be asked. 



Nevertheless, the genes can be maintained only 

 through the activity of the cytoplasm; they are 

 dependent upon it for everything necessary to their 

 existence. In some cells the cytoplasm becomes 

 extremely specialized. Its differentiation may be 

 associated with relatively few genes, yet it con- 

 tinues to provide the proper environment for the 

 full complex of genes belonging to the species. 

 Elsewhere in the body other highly specialized 

 cells of an entirely different nature, dependent for 

 their differentiation upon an entirely different set 

 of genes, may be doing the same thing in addition 

 to their special functions. This condition makes it 

 impossible to avoid the conviction that even though 

 control over development is exercised by a gene 

 only within the including cell, the body must pro- 

 vide a universal basis for the maintenance of the 

 genetic complex, in which every cell takes part and 

 upon which its special characteristics, be they a 

 matter of normal differentiation or of mutation, 

 are superimposed. Continuity in descent cannot 

 be denied, even though it may be freed from Weis- 

 mann's interpretation. If a change in a chro- 



