^4 KANSAS UNIVERSITY SCIENCE BULLETIN. 



bell of this stage are sufficiently clear in their evidence of the 

 nature of the accessory chromosome, and I have not included 

 any number of these stages in the photomicrographs accom- 

 panying this paper. Moreover, in none of the material that I 

 have examined is there any indication whatever of a tetrad 

 structure in the accessory chromosome, and I am thoroughly 

 convinced that it is a univalent chromosome. 



If the earlier prophase of the first spermatocyte be exam- 

 ined, the chief error of Foot and Strobell becomes evident. It 

 is claimed by these investigators that the accessory chromo- 

 some behaves during the prophase as do the other chromo- 

 somes and that there is but a single nucleolus-like body present 

 — a plasmasome. The work of Miss Pinney showing the tran- 

 sition in form and size of the accessory chromosome and of the 

 plasmasome, both of which appear simultaneously in the nu- 

 cleus, makes it entirely clear that Foot and Strobell were mis- 

 taken on this point. As I have elsewhere pointed out, the 

 technic of these investigators is responsible for their failure 

 to find the plasmasome, for it is this structure, and not the 

 accessry chromosome, that is missing from the smear prepa- 

 rations. 



These investigators have pointed out the large difference 

 between the appearance of the accessory chromosome in draw- 

 ings made by Wilson and the photographs illustrating their 

 own paper. Such variations in the form of this element will 

 receive explanation in part from the series of drawings made 

 by Miss Pinney to illustrate the transition in form of the pro- 

 phase elements. Both the stage of development and the method 

 of preparation influence the form of this accessory chromo- 

 some. As a rule, sections show this element as a. spheroidal, 

 apparently homogeneous body during most of the prophase, 

 but occasionally, just succeeding synizesis, it appears as a short, 

 thick thread, with a tendency to be bent at the middle. This 

 is the nearest approach to a spireme condition that it attains, 

 and in this corresponds to similar conditions which I have de- 

 scribed for certain Locustids. So far as my experience goes it 

 would seem to be the rule that the accessory chromosome, to a 

 certain degree, undergoes a granular diffusion of the chromatin 

 similar to that of the other chromosomes, but that it is less ex- 

 tensive and is frequently marked by the close approximation of 

 divisions of the thread. 



It will be observed from plate LXX, figures 4-6 and 11, that 



