80 THE PROBLEMS OF EVOLUTION 



that the chromosomes actually produce the sub- 

 stance. A few cells, notably the spermatozoa, have 

 the cytoplasm greatly reduced, but in every case, 

 natural or experimental, that has been noted, the 

 nucleus is associated with at least a small amount 

 of cytoplasm. 



Neither does the cytoplasm have the power to 

 exist independently for more than a short time. 

 The red blood corpuscles of mammals lose their 

 nuclei in the course of development, but they are 

 short-lived and are constantly being destroyed and 

 replaced. Protozoa may be deprived of their nuclei 

 artificially and may continue to live for a time as 

 masses of cytoplasm, but they are incapable of 

 normal anabolism. Their activity seems to be due 

 to the residuum of potential energy persisting from 

 their nucleate stage. 



It is evident that the present state of our knowl- 

 edge permits only the conclusion that nucleus and 

 cytoplasm are coexistent. We do not know the 

 nature of their interaction, but a significant fund 

 of information enables us to establish satisfactory 

 working hypotheses concerning the essential de- 

 tails. 



In the latest summary of this question known to 

 me, Conklin mentions the uncertainty which pre- 

 vails, but in quoting Morgan's statement: "While, 

 then, we may not be warranted in speaking of the 

 genes as enzymes, the genes may be protein bodies, 



