20 . HARLEY N. GOULD 



to form the atypical sperm. Since there have been some con- 

 flicting accounts of the origin and development of the atypical 

 elements it has been thought worth while to follow their devel- 

 opment in C. plana. 



A. The atypical series. The question of the atypical sperma- 

 tozoa of Molluscs has had the attention of investigators from 

 time to time since 1837, when they were discovered in Palu- 

 dina by Von Siebold. Three of the latest articles on the subject, 

 viz., those of Kuschakewitsch ('13), von Kemnitz ('M), and 

 Reinke ('14) give historical reviews of the work of previous 

 authors. 



There has been the widest speculation as to the function of the 

 atypical elements but no conclusive proof. Goldschmidt ('16) 

 believes that these structures in Molluscs and probably similar 

 ones in Insects are functionless by-products. 



Tw^o views have arisen in regard to the origin of the atypical 

 sperm. Meves ('03), Stephan ('03), Kuschakewitsch and others 

 find their origin similar to that of the true spermatozoa, their 

 development divergent in various degrees from true spermato- 

 genesis. Reinke on the other hand concludes that the apyrene 

 sperm of Strombus do not come from spermatogonia at all, but 

 from 'basal cells,' accessory elements of the testis; and that 

 their development is not comparable to spermatogenesis. Reinke 

 rejects the use of the terms 'apyrene spermatocyte' and 'apyrene 

 spermatid' on account of the restricted meaning of 'spermato- 

 cyte' and 'spermatid' which refer to maturation phenomena. 

 He designates the cell the 'apyrene spermatoblast' from its first 

 appearance to the breaking down of the nucleus and scattering 

 of the centrioles, and the 'apyrene spermatosome' during the 

 subsequent changes up to the adult apyrene spermatozoon. 



Although the origin of the apyrene sperm in Crepidula is not 

 the same as that described for Strombus, and the end-product 

 has an altogether different structure, the early developmental 

 stages, at least, are so similar that it has been decided to retain 

 Reinke's terms for the periods of differentiation, viz., 'spermato- 

 blast' and 'spermatosome.' It is to be understood, however, 

 that while the spermatoblast stage of Reinke begins with a cell 



