44 McCLUNG. 



cidation of other structural peculiarities the relations might be re- 

 versed. By studying, therefore, an extensive collection of nearly 

 related forms, it is possible to draw a composite outline of a proc- 

 ess which will be found applicable in its main features to all the 

 members of the group concerned. 



This fact is taken advantage of in the series of studies upon 

 insect spermatogenesis now being pursued by myself and stu- 

 dents. Instead of taking one species and endeavoring immedi- 

 ately to make out the entire series of processes which character- 

 ize its spermatogenesis, we have considered restricted questions, 

 and have chosen such species as would offer the best facili- 

 ties for answering these. Thus, in the case of the accessory 

 chromosome, it has been found advantageous to trace its course 

 through the spermatogonial divisions in Brachystola, and through 

 the spermatocyte changes in Hippiscns. Probably the sper- 

 matid transformations will demand another form for their best 

 exemplification. 



The danger involved in such a method is the liability which it 

 offers toward accumulating a series of observations upon excep- 

 tional or strongly modified types. This has been guarded 

 against, as far as possible, by verifying the appearances of one 

 form by those manifested in others. While the work thus far 

 done indicates considerable variations in the details of the different 

 processes, it does not seem to suggest any wide deviations from 

 general principles, so that the danger of error in the direction 

 of exceptional instances would not appear to be great. 



A recognition of the accessory chromosome as such is of very 

 recent date and the literature upon it is therefore not very exten- 

 sive. And while its chromosomic character has, in a number of 

 instances, been appreciated and even its participation in the su- 

 preme division act of the chromosomes in the metaphase noted, 

 the mere resemblance in general features to the nucleoli has suf- 

 ficed to caused its inclusion in the group of these questionable 

 bodies. A majority of the references to it will accordingly be 

 found in the literature devoted to a consideration of the nucleoli, 

 and in only a few cases will it be found discussed as a chromo- 

 some. 



On account of the scantiness of the literature, it has been 



