108 NICHOLS— SPERMATOGENESIS ONISCUS ASELLUS LINN. [ApriU, 



than the width. Indeed Hacker himself says of this object that it 

 is not adapted to the solution of the problem of reduction. The 

 like may be said of Artemia. 



With Brauer's results on Branchipus, those obtained with Oniscus 

 likewise do not agree. The double longitudinal split claimed by 

 Brauer for the chromosomes of Branchipus is not shown in the 

 figures with the clearness that might be desired. An oblique view 

 of an elongated chromosome in Fig. 8 shows it to be split longitu- 

 dinally, not twice but only once. In the absence of direct evidence 

 to the contrary, the Figs. 8 and 9 might be explained equally well 

 on the assumption that the twelve tetrads represent two univalent 

 chromosomes longitudinally split and joined end to end. 



In Oniscus, inasmuch as the first division separates two originally 

 distinct chromosomes and the second presumably divides the chro- 

 matin longitudinally, the manner of reduction resembles that of 

 Insecta as described by Henking (i890-'92), Paulmier (1899) and 

 Montgomery (1898, '99). 



If my interpretation of the method of reduction in Oniscus be 

 correct, and that of Riickert concerning reduction in Cyclops be 

 equally so, it becomes clear that the cell generation in which the 

 true reduction takes place need not be the same for all members of 

 a given class of animals. The order in which the reduction and 

 equation divisions take place is, therefore, relatively unimportant ; 

 the significant thing, so far as our knowledge at the present day 

 goes, appears to be that in the Arthropods both divisions should 

 take place. Further research alone can show whether the apparent 

 cases of transverse division in the first spermatocytes of Astacus, 

 Crangon and Branchipus are really such. To the future must also 

 be left the question as to which method of reduction, the Copepod 

 or the Isopod type, is the rule among Crustacea. 



M. Louise Nichols. 



January 10, 190 1. 



