STUDIES ON SEX IN CREPIDULA 39 



and in proportions of about 6 eupyrenes to 1 apyrene. In sec- 

 tions one may observe, however, that there are not always the 

 same proportions in all parts of the goniduct. Near the distal 

 end of the vesicle the proportions of apyrenes increases until 

 they greatly outnumber the eupyrenes, and in the vas deferens 

 beyond the sperm are almost all apyrene. It is probable that 

 this is the result of a lesser motility on the part of the apyrene 

 sperm; for the true spermatozoa which have got into the vas 

 deferens have probably escaped to the exterior; while the more 

 sluggish apyrenes are left in a group which fills up the passage 

 of the vas deferens, even making a plug at the distal end of the 

 vesicle. 



As long as spermatogenesis goes on uninterruptedly ^he vesicle 

 is kept packed full of spermatozoa. Relatively few specimens 

 give evidence that the contents of the vesicle have been recently 

 discharged in copulation. There are so many more males than 

 females in the colonies that this is not surprising. When the 

 testis begins to undergo the regressive changes which have been 

 described in the history of the gonad, the majority of the male 

 germ cells from the sperhiatocyte stage on complete their de- 

 velopment and are passed into the seminal vesicle as adult 

 spermatozoa. Wlien the gonad has become inactive the vesicle 

 may be still full of sperm and the individual able to function 

 as a male if the i>enis has not begun to degenerate. The relative 

 condition of the different organs during the period of regression 

 is shown in table 3. The ten specimens in the table are se- 

 lected out of about 75, to give the most representative 

 conditions. 



Degeneration of the accessory male organs, a. Seminal vesicle. 

 The manner of the disposal of the spermatozoa which c^re left 

 in the seminal vesicle after the testis is no longer active, is in- 

 teresting (figs. 69 to 72). The enclosing wall of the vesicle 

 becomes somewhat thicker and its tissue becomes looser and more 

 vacuolar. The sperm then begin to penetrate into it (fig. 69). 

 A part, at least, of the middle piece of the true spermatozoon 

 may enter into the wall with the head, for it can be seen embedded 

 in the cytoplasm after the head has gone in; it is uncertain 



