STUDIES ON SEX IN CREPIDULA 27 



easy to see why they should not be found there, especially if the 

 hypothesis of Giese is correct that the slender tip of the penis 

 is inserted directly into the seminal receptacles; for in that case 

 the ciliary action in the sperm groove of the male would probably 

 carry the apyrenes along with the true sperm. The apj^renes 

 are not so large nor so awkwardly shaped that they could not go' 

 into any aperture that the eupyi'enes would be likely to pass. It 

 is possible that the apyrene spermatozoa are passed into the 

 seminal receptacles of the female, but that they speedily de- 

 generate. 



In smears taken alive from the seminal vesicle of the male, the 

 apyrene sperm are seen to have a serpentine movement. They 

 are not always in motion; some may be quiescent for a time, fol- 

 lowing which a wave-like movement proceeds rapidly from one 

 end of the sperm to the other. After having been on the slide 

 for some time the quiescent periods become longer and longer, 

 and the movement less and less frequent. The eupyrene sperm, 

 of the other hand, continue to move constantly, although more 

 and more slowly until they cease entirely. The eupyrene sperm 

 when left on the slide for some time will agglutinate; the apyrenes 

 never do. 



Giese ('15) has described the atypical spermatozoa of Crepidula 

 unguiformis as 'oligopyrene,' i.e., with a small amount of chro- 

 matic material persisting in the adult structure (Meves). The 

 three American species of Crepidula all have 'apyrene' sperm 

 (without chromatin when adult). Giese's figure of the adult 

 atypical sperm of C. unguiformis exactly resembles an imma- 

 ture stage in C. plana. Furthermore, Giese mentions a ''fib- 

 rous secretion of unknown origin" in the seminal vesicle. It is 

 suggested that he failed to recognize the adult apyi'ene element. 



The development of the atypical spermatozoa in Crepidula 

 differs from most of the other forms which have been described 

 in that the spermatoblast does not outstrip the eupyrene sperma- 

 tocyte during the growth period. On the contrary the spermato- 

 blast and spermatosome remain about the same size as the fully 

 grown spermatocyte, until the cytoplasm begins to apply itself to 

 the axial bundle. 



