92 bulletin: museum of comparative zoology. 



Going outside the follicle, it is of interest to note what appears in 

 the nuclei of the follicular investment. This investment is a thin 

 membrane inclosing the follicle, forming the outer of the two laj^ers 

 composing the follicular wall. In this membrane the nuclei are very 

 much flattened, so that the chromosomes lie nearly all in one plane. 

 Figures 111 and 112 indicate the chromatic conditions in two such 

 nuclei. It is, I believe, a significant fact that the chromatic masses 

 to be found in these nuclei are in number approximately equal to the 

 unreduced number of chromosomes found in the spermatogonia. 

 Exceptions, it is true, occur; adjacent cliromosome-masses may be- 

 come intunately associated, or one individual mass may become 

 divided into partially separated masses. These nuclei are fully 

 differentiated and are destined never to undergo another cell-division. 

 They must gradually lose their functions and will finally " die in their 

 tracks." The different conditions of the chromatin in the different 

 nuclei suggests that the process of senescent degeneration may have 

 already set in. The important fact still remains, that the individual 

 chromosomes have a tendency to remain distinct from each other, 

 even in these highly differentiated nuclei in a period not only of 'rest' 

 but perhaps of senescence. 



D. Summary of Observations. 



1 . The general topographical relations of the different generations 

 of male sexual cells in the testes of Phrynotettix magnus are typical 

 for the Acrididae. 



2. For purposes of accurately following the history of the changes 

 undergone by the chromosomes from the pachytene stages of the first 

 spermatocyte to the time of mitosis, three individual chromosome- 

 pairs were selected, each of which possessed characteristics by which 

 it could be recognized in all the stages concerned. These three pairs 

 were designated, for convenience, "A," " B," and "C." A study of 

 these three chromosome-pairs showed : — (a) that there is a longi- 

 tudinal split in the pachytene stages, which persists into the tetrad 

 and later stages (this is called the primary longitudinal split); (b) 

 that a tetrad is formed out of a spireme segment by (1) a separation 

 along the primary split, and (2) the appearance of a secondary longi- 

 tudinal split along the middle of each of the two parts separated by 

 the primary split. 



3. Tetrad " ^ " opens out along the plane of the secondary split. 



