74 ROBERT H. BOWEN. 



sections which are very similar to mine, except that there is never 

 more than one thread in each half of the nebenkern at any stage. 

 Subsequently the chromophobic material is said to disappear and 

 the threads themselves finally dissolve leaving no trace of mito- 

 chondrial substance in the mature sperm. This account of the 

 fate of the threads and the nebenkern substance as a whole is 

 negatived by more recent studies on the role of the mitochondria 

 in sperm formation. As to the mode of origin described by 

 Holmgren, it seems to me not improbable that technical faults 

 caused him to overlook the early history of the threads, and at the 

 time when he first demonstrated them their development was al- 

 ready well advanced. 



In Diestrammcna, according to Vejdovsky ('12), the nebenkern 

 has at firsr the characteristic division into a central chromophilic 

 substance and an enveloping zone of chromophobic material. 

 Cross-sections of this stage are quite similar to mine except that 

 the axial filament is represented as piercing the center of the chro- 

 mophilic core. This is a very unusual condition, if true, the cus- 

 tomary position of the filament being in or near the cleft of the 

 nebenkern, but outside of the substance of the nebenkern itself. 

 (Compare my Figs. 21 A and B, and 22 with Vejdovsky's Figs. 

 iSie, /, g.} Presently there appears in the chromophilic ma- 

 terial a number of separate,, intensely staining granules which be- 

 come arranged in rows parallel to the axial filament ; and eventu- 

 ally the chromophilic material is entirely replaced by spirally 

 wound (later beaded) threads. The end result is strikingly like 

 that in the Hemiptera. Vejdovsky believes that the process is 

 to be interpreted as a transformation of the " Chondriom" (chro- 

 mophilic substance) into the granular components ("Mitochon- 

 drien ") from which it originally arose. According to this view 

 the threads would be secondarily a differentiation product of the 

 chromophilic material itself a view somewhat similar to that of 

 Holmgren. The beaded appearance of the threads marks, ac- 

 cording to Vejdovsky, the breaking up of the threads, the granu- 

 lar products (Mitochondrien) thus formed swelling up to a large 

 size and being simultaneously transformed into a fat-like sub- 

 stance. These fat droplets seem to fuse together to form larger 



