714 



THE AMERICAN NATURALIST 



[Vol. LI 



not know much about the growth of the egg and embryo- 

 logical development of this genus of flies, we do know that 

 these processes in certain other flies resemble those of 

 beetles. 



If the Mendelian factors are located in the chromo- 

 somes, it is evident that they may exert an influence upon 

 the entire contents of the egg, (1) during the mitotic divi- 

 sions of the oogonia, (2) during the so-called resting 

 stages of the oogonia, and (3) during the growth of the 

 oocytes. It is also clear that all of the factors carried by 

 the chromosomes have an equal opportunity to interact 

 with the cytoplasm and not alone those that remain within 

 the egg after the elimination of chromosomes during 

 maturation. The adult, however, that develops from the 

 egg, whether fertilized or unfertilized, exhibits only those 

 detailed characteristics whose genetic factors are sup- 

 posed to be located in the chromosomes remaining in the 

 egg after maturation, or in those that are brought in by 

 the sperm. This seems to indicate that none of these 

 factors has any permanent influence upon the egg organi- 

 zation during the growth of the oocyte and until matura- 

 tion is completed. 



It seems impossible to ignore the chromosomes or even 

 to locate the principal factors of heredity in any other 

 cell bodies. It may therefore be necessary to reconstruct 

 our ideas of chromosome architecture and thereby aban- 

 don the theory that these bodies consist of a linear series 

 of factorial determiners for certain ferments and of noth- 

 ing else. It may be possible to separate our hypothetical 

 factors into two groups, (1) those responsible for such 

 characteristics as the polarity, bilateraUty and "pattern" 

 of the egg, and (2) those that control mutations that ap- 

 pear at a late period in the life history like those that are 

 so abundant in Drosophila. Perhaps the latter may be 

 anchored to the chromosomes as has recently been sug- 

 gested;^^ the main portion of the chromosomes might then 

 represent the foundation for the factors responsible for 

 the organization of the egg and the attached masses of 



