STUDIES ON INSECT SPERMATOGENESIS. 67 



partition (Fig. 13). If the spermatic! be viewed at right angles 

 to the plane of division of the nebenkern (i.e., at right angles to 

 the plane of Fig. 13), the central chromophilic mass appears as a 

 single, regular plate (Fig. 14). 



Slightly later the chromophilic core has shrunk still further 

 (Fig. 15) and finally it becomes so much reduced as to be barely 

 visible as a purple-staining (after Benda) patch within the neben- 

 kern proper (Fig. 16). As the nebenkern begins actively to 

 elongate, the last remnant of the chromophilic material vanishes 

 (Fig. 22) and no trace of it can be found at any subsequent stage. 

 It has disappeared apparently by a process of gradual solution in 

 the chromophobic substance. 



The gradual breaking down and disappearance of the "onion" 

 stage has been noted by several previous workers ; and still others 

 have figured several o>f the later stages without apparently any 

 very accurate idea of what was occurring. Henking ('91) de- 

 scribed the process in Pyrrhocoris, the layers of the onion stage 

 gradually disappearing from without inward by fusing together, 

 leaving at length a small, dark point in the center of the neben- 

 kern which likewise disappears. Gross ('07), working on the 

 same form, has given a slightly different account, less accurate 

 in some respects than that of Henking. Boring ('07) has clearly 

 figured, (Figs. 304 and 313) the intermediate condition of my 

 Figs. 7 and 8 in Aniphiscepa and Pceciloptera, while the very 

 regular arrangement of the chromophilic substance in its later 

 phases of dissolution is well figured by Doncaster and Cannon 

 ('20) in Pediculus. It is of interest in connection with these last 

 named observers, that they made a conscious effort to find a 

 " spireme " like that described by Gatenby, but failed entirely. 

 Their figures indicate a course of events similar to that in the 

 Pentatomida. Many other workers have figured what appear to 

 be these later stages in the history of the chromophilic substance, 

 but these need not be dwelt upon here since it is uncertain whether 

 they are to be considered as the end stage of the plate-work type 

 of nebenkern or an artifact from a spireme structure. These fig- 

 ures have the common characteristic of a clear peripheral envelope 

 containing a chromophilic central mass'. (See, for example, the 



