STUDIES ON SEX IN CREPIDULA 37 



rection. In sexually inactive animals the duct runs nearly- 

 straight from the gonad to the mantle cavity. 



Development of the accessory male organs, a. Seminal vesicle 

 and vas deferens. As soon as the male development of the 

 gonad is well under way, the efferent duct differentiates into 

 two regions: a proximal, widened, convoluted seminal vesicle, 

 and a distal, narrower vas deferens. Figure 66 shows the 

 proximal part just as it begins to widen. In this specimen the 

 newly forming seminal vesicle was only just beginning to twist 

 upon itself. A more advanced stage is seen in figure 67; the 

 seminal vesicle has a number of turns, and the figure is an 

 oblique section across one of them. The testis has produced 

 some adult eupjTene and apyi-ene sperm, of which a few have 

 made their way to the vesicle. Figure 68 shows the more distal 

 part, or vas deferens, of the same goniduct. It has retained 

 more of the primitive character. 



b. The penis. In the meantime the penis has appeared as a 

 small hump behind the right tentacle of the individual which is 

 assuming the male phase. There is not the least sign of it so 

 long as the gonad remains in an inactive condition, regardless of 

 age or body size. Most of the stages of spermatogenesis are 

 usually to be found in the testis before the penis becomes very 

 prominent. Its growth is very rapid, however, and it may reach 

 its full size within a few days, as will be shown later. When 

 fully formed it is about three-fourths of the length of the entire 

 body, a long, muscular organ with a slender tip. Its histological 

 structure has been sufficiently described in formis nearly re- 

 lated to C. plana, by former authors (Haller, '92; Vayssiere, '93; 

 Scheidig, '13; Kleinensteuber, '13; Giese, '15). During the 

 outgrowth of the penis the seminal groove is formed along the 

 right side of the neck by a sitiking in of epithelial cells and the 

 acquisition of cilia on their free surface. The position and struc- 

 ture of the sperm groove has also been described by the authors 

 above cited. 



Time of development of the male organs. The signs of male de- 

 velopment always appear in the testis before they are evident in 

 the accessory organs of reproduction. The development of the 



