STUDIES ON SEX IN CREPIDULA 41 



whether the flagellum, which is very long in the eupyrene sperm 

 of Crepidula, also penetrates or is left outside and dissolves in 

 the lumen. Figure 70 shows a part of a vesicle filled with 

 sperm of both kinds, where many eupyrene sperm heads have 

 penetrated into the wall, and whatever part of the sperm body 

 has also entered has dissolved. The sperm heads are often 

 clumped together, and twisted about each other like the strands 

 of a rope or like twisted synaptic threads. The clumps and the 

 single sperm heads often though not always lie in clear vacuoles. 

 The apyrene sperm as well as the eupyrenes get into the wall 

 of the vesicle (figs. 71, 72). 



There are indications that the entrance of the sperm into the 

 wall is brought about partly by the motility of the sperm and 

 partly by the amoeboid movements of the cytoplasm. The 

 process is undoubtedly the same as we have already seen in the 

 testis during its degeneration. 



The sperm do not all remain alive till they are enclosed in the 

 wall of the vesicle; some die and degenerate in the lumen (see 

 specimen 56, table 3). 



Of the sperm which are taken up by the wall of the vesicle, 

 the apyrenes and the non-chromatic part of the eupyrenes are 

 dissolved first; while the eupyrene sperm heads remain for some 

 time longer, finally assuming a beaded and shrunken appearance 

 (fig. 72) in the process of dissolution. The fact that some live 

 spermatozoa remain in the lumen of the vesicle after most of the 

 contents have been taken up and dissolved by the walls indicates 

 that there is no substance liberated in the lumen which is fatal 

 to the adult spermatozoa, but that there is a change in the cyto- 

 plasm of the vesicle cells, which allows the sperm to penetrate 

 the wall more easily, and in fact assists the penetration; after 

 which the cytoplasm may kill and dissolve the sperm. The same 

 may be said in regard to the testis; but there is some change in 

 the testis which affects the immature testicular elements in the 

 lumen, particularly the spermatogonia and early spermatocytes, 

 so that their development can no longer be completed. 



Cilia are hard to distinguish on the inner surface of the vesicle 

 as long as the lumen is filled with sperm, though they are prob- 



