STUDIES ON SEX IN CREPIDULA 119 



able to act in the absence of physical contact and through several 

 millimeters distance in sea-water. A comparison with other ex- 

 periments indicates that fewer and less fully developed males are 

 produced under such conditions than when the stimulus acts 

 more directly. 



The writer has tried several times to determine whether a 

 large female of Crepidula fornicata, another species of the same 

 genus, could furnish the stimulus for male development in a small 

 neuter Crepidula plana. The experiment has been difficult to 

 carry out, as the little C. plana neuters were ger\jerally crushed by 

 the twisting and turning movements of the great C. fornicata 

 before sufficient time elapsed to make the experiment valuable. 

 The writer has, however, slides made from thirty-two C. plana 

 selected as neuters and kept near the C. fornicata for various 

 periods. Of these, twenty-one remained entirely neuter and six 

 became incipient females. The remaining five show traces of 

 male development. Two of these must be counted out because 

 the microscopic appearance of the gonad shows that the few prod- 

 ucts of spermatogenesis there must have been formed and fur- 

 ther activity must have ceased before the experiment began. 

 This leaves only three which seem to have developed any male 

 characters during association with C. fornicata, and they are as 

 follows : 



a. Penis partly developed and small testis as far as spermatids, 

 not very active. Time, seventeen days. 



b. No penis. A few spermatogonia and spermatocytes. Time, 

 eleven days. 



c. No penis. Spermatogonia and a few spermatocytes. Time, 

 eight days. 



Thus, there are no adult males developed out of twenty-six 

 neuter specimens (leaving out of consideration those which 

 had begun female differentiation) , but there are three with partial 

 male development during the experiment. This result is rather 

 perplexing. One would naturally expect either an appreciable 

 proportion of males, if the C. fornicata exerted any influence, or 

 none at all, if they did not. However, we may draw the conclu- 

 sion that the male-producing stimulus is not due to any general 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 29, NO. 1 



