100 XICHOLS — SPERMATOGENESIS OXISCUS ASELLUS LIXN. [April 4. 



Open and regular ring. The close relationship of nucleus and cyto- 

 plasmic fibre in Oniscus is shown only in Fig. 320. In Figs. 323 

 and 326 they are represented as discontinuous. In Fig. 334 

 (Asellus) the fibres are pictured as arising independently of the 

 nuclei, although it is shown in later figures that they eventually 

 become attached. If the follicle nuclei and the surrounding proto- 

 plasm take part in the formation of the tails, it is only, in my opin- 

 ion, in so far as they become converted into the substance of the 

 germ cells. 



In attempting to reconcile the fact of the direct continuity of 

 head and tail, shown by Gilson so clearly in Asellus and stated by 

 him to be present in Sphaeroma, with the lack of demonstrable con- 

 nection in Oniscus, it occurred to me that the condition in Oniscus 

 might represent a different phase in the evolution of the Isopod 

 spermatozoon. Either the connection, at one time evident, between 

 the nucleus and the unusually long tail may have grown so slight as 

 to be no longer recognizable, or, if the spermatozoon of Oniscus 

 for any reason is to be looked upon as the more primitive form, it 

 may be that the connection, which will later in the course of evolu- 

 tion become more marked, is as yet but little developed. Although 

 in the present state of our knowledge both alternatives may perhaps 

 be considered open, the former seems to me far more plausible, for 

 not only are the land Isopods in other structural peculiarities to be 

 regarded as more specialized than Asellus, but the sperm colony 

 itself in Asellus is less compact and less completely developed as a 

 unit. The obscurity of this point serves to emphasize the desira- 

 bility of further study of the Crustacean spermatozoa and the estab- 

 lishment of accurate homologies between them. 



The " noyau femelle" of Asellus is, in my opinion, to be regarded 

 as homologous with the follicle cells of Oniscus. I am inclined to 

 doubt the correctness of M. Gilson's conclusions as to the origin of 

 the small cells of the vas deferens of Oniscus from the larger ones 

 by segmentation, and, although I have not devoted much time to 

 the elucidation of the point, I think it more probable that the re- 

 verse is true, for I have seen the small cells segmenting, but never 

 the large ones. 



