36 Edmund B, Wilson 



activity in the two cases, incited by intra-cellular conditions that 

 are external to the chromosome-groups; and a similar explana- 

 tion may apply to the related case of the formation of visibly 

 different female-producing and male-producing eggs in the same 

 organism. 



It would not, I think, be profitable to speculate further in regard 

 to these special cases, but I have wished to indicate that a hypo- 

 thesis of sex-production which recognizes in some cases a fixed 

 predetermination in the chromosome-groups of the fertilized egg 

 is not inconsistent with the control of sex-production in other 

 cases by conditions external to the nucleus. The constant 

 chromosomal differences of the sexes existing in many Hemiptera, 

 therefore, by no means preclude experiments on the modification 

 or control of sex-production. 



I have intentionally excluded from the foregoing suggestions 

 any discussion of the specific nature of the activities of the differen- 

 tial chromosomes, since we are almost wholly ignorant of the 

 functions of chromosomes in general. But although we here 

 enter upon still more debatable ground, I think we should not 

 hesitate to consider such possibilities in this direction as the facts 

 may suggest. 



One of the principal, or at least most obvious, differences 

 between the germ-cells of the two sexes is their great contrast in 

 constructive activity, evinced by the enormous growth of the 

 primary oocyte as compared with the primary spermatocyte. 

 This growth of the oocyte involves the production of a mass of 

 protoplasm (including under this term the yolk or metaplasm as 

 well as the active protoplasm) thousands of times the bulk of the 

 spermatocyte; and although the latter also increases noticeably 

 in size during the growth-period, the accumulation of proto- 

 plasm is almost insignificant as compared with that which takes 

 place in the female. Now, as described above, the idiochromo- 

 somes and heterotropic chromosome remain during this period in 

 the male in a relatively passive condition as compared with the 

 other chromosomes, while this is not the case in the female. The 

 thought cannot be avoided that there is a definite causal connec- 



o 



tion between the greater activity of these chromosomes in the 



