INFLUENCE OF ENVIRONMENT ON SEX 249 



probably never occur,s ; but if at any time up to the female stage 

 the small individual comes within the sphere of influence of a 

 larger one, it will immediately develop male organs, attaining the 

 male condition in about two weeks. Whether or not the male 

 phase is realized, the female phase is eventually developed. 



The degeneration of the male organs does not prevent a second 

 or third male development if the small Crepidula comes within 

 the sphere of influence of a larger one after the degeneration. 

 Partial degeneration may be halted and male activity resumed. 



During the male phase the growth of the body is retarded; 

 after degeneration of the testis and during the sexually inactive 

 condition, or in neuter animals which have never developed the 

 male condition, growth is rapid. 



The first steps of female development may be interrupted and 

 replaced by male development, under experimental conditions. 

 In this case the oocytes degenerate and the acti\dty of the pri- 

 mordial female cells is suspended ; while the primordial male cells 

 multiply and undergo maturation. After the oocytes are ad- 

 vanced in the growth period, male development is no longer 

 possible. 



The nature of the stimulus to male development in C. plana is 

 at the present time not certainly known. The following state- 

 ments may be made in regard to it: 



1 . The stimulus depends upon the presence of the actual body 

 of a large Crepidula plana; for if the large specimens be re- 

 moved, leaving all the other conditions of the colony unchanged 

 (even the shells of the large specimens still in their former 

 positions) the stimulus is no longer given. 



2. The movement of the smaller individuals, from whatever 

 cause, does not furnish the stimulus ; for some males are developed 

 while in a fixed position. 



3. Male development does not depend upon the amount of 

 food received; for starved neuter specimens develop a testis as 

 quickly as well-fed ones, when in the presence of large females; 

 and they do not develop any more quickly. 



4. No experiment has so far demonstrated the existence of a 

 stimulating secretion; this possibility has not been thoroughly 

 tested. 



