120 HARLEY N. GOULD 



change in the medium (sea-water) caused by C. plana which 

 would be similarly caused by other species. The C. fornicata 

 females used for the experiment were larger than the largest C. 

 plana females, and would be expected to throw into the sea- 

 water at least as much of the general katabolic products, for in- 

 stance, as the latter, yet they had almost no effect in stimulating 

 development of the testis. 



It should be emphasized that the power of large animals of the 

 species C. plana to stimulate spermatogenesis in the smaller is not 

 limited to females. A number of unusually large males were 

 removed from a colony and imprisoned in a watch crystal w4th 

 nine small neuters. In eighteen days five of the nine showed 

 some degree of male development, mostly immature. The large 

 males were in the meantime losing their male characters. They 

 were kept forty days after this losing all signs of maleness and 

 growing larger. A second lot of nine small neuters was placed 

 with them. In sixteen days eight of the nine had some degree 

 of male development, averaging nearer the mature male phase 

 than the first nine. The numbers are too small to speak for the 

 relative effectiveness of large males and large transitionals, but 

 show the ability of both to produce the stimulus. 



SUMMARY 



The stimulus passing from larger to smaller Crepidula plana, 

 causing the latter to assume and retain the male phase, can be 

 transmitted for several millimeters through sea-water, though its 

 effectiveness is reduced at this distance. Indication that the 

 stimulus may be given faintly by Crepidula fornicata, a related 

 species, was given in only three out of twenty-six cases. 



The stimulus acts in such a manner as to suggest that it is a 

 specific substance given off from the bodies of the animals, dif- 

 fusible in sea-water, but very unstable. 



BIBLIOGRAPHY 



Gould, H. N. 1917 Studies on sex in the hermaphrodite mollusc Crepidula 

 plana. I. History of the sexual cycle. Jour. E.xp. Zool., v. 23, no. 1. 

 II. Influence of environment on sex. Jour. Exp. Zool., v. 23, no. 2. 



