INFLUENCE OF ENVIRONMENT ON SEX 247 



In view of the negative results of the above mentioned experi- 

 ments, the writer does not wish to do more than suggest the 

 possibihty of a chemical stimulus, until the point has been 

 further investigated. 



GENERAL CONSIDERATIONS 



It must be understood that the peculiar condition which has 

 been found in Crepidula plana, the dependence of the male 

 phase on conditions of the environment, has been developed 

 within the species. So far as the writer is aware no similar 

 phenomenon has been described in any other Mollusc. Small 

 specimens of the nearly related Crepidula convexa and Crepi- 

 dula fornicata have been kept in aquaria by the writer, in the 

 absence of larger specimens of the same species, under the same 

 conditions as the segregated individuals of C. plana; yet the 

 treatment did not interefere with the development and main- 

 tenance of the male phase. Many specimens were fixed and 

 sectioned which had been found living in nature where no larger 

 ones were in the vicinity; those of the 'male sizes' had fully 

 developed, active testes. Apparently, then, the peculiarity of 

 C. plana is a special and not a generic one. It is true, how- 

 ever, that there is great variation in the activity of spermato- 

 genesis in C. convexa and C. fornicata. Occasionally specimens 

 are found (not necessarily segregated) where the gonad is very 

 nearly inactive. It would be interesting to learn whether the 

 European and South American species of Crepidula show any 

 sexual behavior similar to that of C. plana. 



Outside the Molluscs there is one striking instance of sexual 

 behavior somewhat similar to that which the writer has found. 

 Baltzer (10) in investigating the development of the marine 

 worm Bonellia viridis, has found that if the free-swimming larva 

 attaches itself to a female of the same species, and develops there 

 in a parasitic manner, it becomes a male; but that if it develops 

 solitarily, it becomes a female. 



The case of Bonellia is clearer than that of Crepidula plana, 

 in that there is an actual contact between the animal which gives 

 the stimulus to male development and the animal which receives 



