1902.] NICHOLS— SPERMATOGENESIS ONISCUS ASELLUS LINN. 107 



arranged in the equatorial plate with the transverse constriction in 

 the plane of the equator. This division consequently is apparently 

 reducing. No longitudinal split is shown and the second sper- 

 matocytic division is very inadequately worked out. 



b. Cofnmentary. 



Although agreeing with many points in the description of Gilson 

 concerning the metamorphosis of the spermatids of Oniscus, my 

 observations do not entirely coincide with his account of the earlier 

 stages. The statement defining the most favorable season for ob- 

 taining preparations of the first stage does not hold true for the 

 locality of Philadelphia, for I have sectioned material collected 

 during every month of the year, except December and January, and 

 have not found one monlh to be preferred over another with regard 

 to the abundance of any particular stage. 



I feel sure that the function of replacing the evacuated elements 

 which he ascribes to the spermatogonia is the true one, but that 

 their multiplication takes place by direct division I am unable to 

 believe. On the one hand the weight of the evidence of modern 

 research is against the occurrence normally of amitotic division in 

 the germ cells. Moreover the work of vom Rath on Astacus creates 

 a strong probability that the phenomena are similar in Oniscus. I 

 have never seen amitotic division in the germ cells of Oniscus, and 

 believe that the error arose from a failure to distinguish between 

 the germ cells and the follicle cells. I cannot help a feeling of 

 surprise that mitosis should have been so infrequently seen both by 

 M. Gilson and his colleague, M. Carnoy. It is true that the 

 mitoses of the spermatogonia are scattered, and occasionally no 

 spindles at all will be met with in a follicle, but by cutting a 

 sufficient number of sections cell division will be abundantly 

 seen. 



With regard to the question of reduction in the Crustacea, my re- 

 sults, much to my own surprise, do not coincide with those obtained 

 by Riickert and vom Rath in the Copepods. The case in Cyclops 

 is so clear that it seems to admit of no doubt, and its very clearness 

 makes it probable that the divisions take place in a similar manner 

 in a form so closely allied as Canthocamptus. The figures given by 

 Hacker of this object do not, however, conclusively prove this to be 

 the case, since the tetrads are cubical in shape, the length no greater 



