276 CALKINS. [Vol. XI. 



The blastophore, therefore, seems merely an excess of cyto- 

 plasm, and evidently is not morphologically the equivalent of a 

 vertebrate Sertoli cell as Bloomfield assumes. The Sertoli 

 cell, according to Watas6 ('92), is derived from the primordial 

 germ epithelial cells ; according to von Ebner ('88) it is derived 

 from a spermatogonium which ceases to divide and is devoted 

 to the absorption of nutriment in the shape of fats, etc., for the 

 use of the developing germ cells. These cluster about and upon 

 the Sertoli cell, where, like parasites upon a host, they com- 

 plete their development. The blastophore, on the other hand, 

 is not a cell, for it has no nucleus. It lives as long as the 

 developing germ cells are connected with it and dies when 

 deserted by the spermatozoa. Nor is there any reason to 

 suppose that it provides nutriment for the spermatic cell. 



It is conceivable, however, that the vertebrate Sertoli cell 

 was derived from some such structure as the Annelid blasto- 

 phore. Both originate from the early spermatogonia or per- 

 haps from the earlier reproductive tissue ; neither of them 

 forms any part of the mature spermatozoon ; the function of 

 the former, however, is clearly defined, while that of the latter 

 is purely conjectural. If, as appears not improbable, the blasto- 

 phore is merely an excess of cytoplasm, the nuclei of the multi- 

 nucleate cell upon migrating to the periphery of this cell must 

 have about them that portion of the cytoplasm which is essen- 

 tial to the formation of the mature spermatozoon. If one of 

 the nuclei should remain behind, the result would be, morpho- 

 logically, a Sertoli cell. 



I have been unable to follow the history of the blastophores 

 after they have been deserted by the mature spermatozoa. Their 

 appearance is so altered that we hardly recognize them as the 

 same substance as the cytoplasm of the spermatid. At this time 

 they resemble more closely the protoplasm of protozoa after dif- 

 fluence. It is probable that their final disappearance is due to 

 atrophy, as suggested by Bloomfield, although many of them 

 serve as food for embryonic parasites [Monocystis) which in- 

 variably infest the seminal vesicles of Lumbricus. 



