226 HARLEY N. GOULD 



and while the analysis is by no means complete, a number of 

 facts have been disclosed which have to do with the influence of 

 environment on sexual development. 



Light was first thrown on the question by the observation that 

 those animals which we may call 'sexually inactive' or 'neuter/ 

 though of a size equal to the males, were most frequently found 

 in the 'new' hermit crab shells (i.e., Gastropod shells only re- 

 cently acquired by the hermit), in which there were only a few 

 small Crepidulas, and no large females. Of 216 specimens taken 

 from such situations, there were 11 males (5 per cent). The other 

 205 (95 per cent) were either immature males, degenerate males 

 or sexually inactive. This could be determined in the live 

 animals by the amount of development or the non-development, 

 of the external sex organs, the penis and seminal groove. The 

 majority of all Crepidulas found in the 'new' shells had the 

 thin, round, smooth shell which is characteristically formed on 

 an unobstructed surface. 



In the large colonies, or in fact in any shell where one or more 

 large female Crepidulas were present with the smaller ones, the 

 proportions were strikingly different. Material of this kind 

 was more abundant and 1066 small individuals were examined, 

 of which 662 (62.1 per cent) were adult males, 404 (37.9 per 

 cent) were either immature males, degenerate males or sexually 

 inactive. 



DEGENERATION OF THE TESTIS 



An accident disclosed another interesting fact. About 50 

 males had been removed from the colonies in the hermit crab 

 shells, and placed by themselves in a dish under running salt 

 water. They were neglected for several weeks and when subse- 

 quently examined seemed to be perfectly normal except that the 

 penis had in every case disappeared, leaving only a small brown 

 hump behind the right tentacle. Sections of the gonad showed 

 that it had shrunken to small strands which ran here and there 

 in the visceral sac. This chance observation coupled itself 

 with the fact that males are far more numerous in large Crepi- 

 dula colonies than in ' new' hermit shells having only a few small 



