INFLUENCE OF ENVIRONMENT ON SEX 



241 



stages and give place to the male phase. Occasional instances 

 found in nature indicate this, and in a few cases the superpo- 

 sition of male on female development has been accomplished 

 experimentallj^ Two such cases are described in table 11. 



Superposition of male on female development. Specimen 313: collected as neuter; 

 placed close to two considerably larger immature fem,ales for eight days. Speci- 

 men 314-: collected as neuter; placed hetvjeen two large females in fingerbowl for 

 nineteen days 



The above accounts for the occasional presence of oocytes in 

 the male gonad of C. plana. It is due to spermatogenesis in- 

 terrupting the first stages of female differentiation. In such an 

 event the oocytes do not persist very long, but if male develop- 

 ment continues, degenerate. Undoubtedly in C. plana the 

 separation of the two sexual phases is an adaptation so fastened 

 upon the species that sperm and eggs cannot develop under the 

 same conditions in the gonad. 



The attempt was made several times to cause nearly adult 

 females to return to the male state. All results go to show that 

 after the oocytes are well on in the growth period no more male 

 development is possible. Careful examination of ovaries was 

 made after the effort to incite spermatogenesis, in order to find 

 whether there were at least any mitoses of primordial male 

 cells; and not only were such mitoses absent, but primordial 



THE JOURNAL OP EXPERIMENTAL ZOOLOGY, VOL. 23, NO. 2 



