ZOOLOGY AND BOTANY, MICROSCOPY, ETC. 577 



seminal vesicles as adult spermatozoa. The rest are absorbed into the 

 wall of the testis, where they are dissolved ; or else they degenerate in 

 the lumen of the gonad. There is a temporary reduction in the size of 

 the gonad ; it becomes large again when the oogonial cells, after a period 

 of division, develop into oocytes and enter upon the growth period. 



The goniduct serves for the transference of both spermatozoa and 

 eggs, but is, structurally, entirely different in the male and the female 

 phases. In the male phase it is differentiated into seminal vesicle and 

 vas deferens. 



The accessory male organs appear only when the testis develops. In 

 the " sexually inactive " animals there is no penis, seminal vesicle, nor 

 sperm groove. These develop very quickly, however, when male 

 differentiation takes place in the gonad. 



During the change from the male to the female condition, or upon 

 the premature loss of the male condition, the penis, seminal vesicle, and 

 sperm groove degenerate. Before its degeneration the seminal vesicle 

 absorbs the contained spermatozoa into its wall, where they dissolve. 



As the female phase is gradually assumed the goniduct increases 

 greatly in size, acquires longitudinal folds and glands in its wall, and 

 becomes the oviduct. At this point in the life-history the " gono- 

 pericardial duct " is also developed, connecting the pericardial chamber 

 with the oviduct. 



Influence of Environment on Sex of Crepidula.*— Harley N. 

 Grould finds that in the protandric hermaphrodite Crepidula plana the 

 development of the male phase is dependent upon the presence of a 

 larger individual, not necessarily a female, of the same species. Some 

 stimulus passes from the larger to the smaller. A small stimulus will 

 initiate the male development, but a greater one is needed to complete 

 and maintain it. When a male is removed from the neighbourhood of 

 the larger animal, the male organs degenerate, a condition of sexual 

 inactivity ensues, later replaced by female development. 



If a larval C. plana settles and grows during the first part of its life 

 where no larger individuals are present, the male phase probably never 

 occurs ; 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 individual comes within the sphere 

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

 may be stopped 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 



* Journ. Exper. Zool., xxiii. (1917) pp. 225-50. 



