68 ROBERT H. BOWEN. 



figures of Holmgren ('02) (Silpha) , Vejdovsky ('12) (Diestram- 

 mena), Shaffer ('17) (Passalus") , and Zweiger ('07) (Forfic- 

 ula}.} 



One further feature which seems to have some relation to the 

 final disappearance of the chromophilic core remains to be con- 

 sidered, viz., the division of the nebenkern into two parts. It will 

 be observed (Fig. 13) that the nebenkern commences to elongate 

 before the chromophilic substance has entirely disappeared, and 

 at the same time there is a marked indication of the longitudinal 

 splitting of the nebenkern into two parts. This division plane 

 seems to deepen as the chromophilic core withdraws more and 

 more toward the center of the nebenkern (Fig. 15), but the divi- 

 sion never extends through the core itself. This is clearly shown 

 in Figs. 2iA and B, which show optical cross-sections of the 

 nebenkern at about the stage of Fig. 15, at two different levels. 

 In Fig. 21 A, the section passes through the chromophilic sub- 

 stance, while in Fig. 2iB it passes above (or below) it. It is clear 

 that the actual division of the nebenkern has extended only to the 

 periphery of the central, chromophilic mass. When this finally 

 disappears, the division of the nebenkern is completed (Fig. 22), 

 and from this point on the nebenkern draws out as two separate 

 bodies the mitochoiidrial sheaths of the tail filament as de- 

 scribed by many authors. It is interesting to note that Henking 

 ('91) observed, after the final condensation of the "pattern," that 

 the two halves of the nebenkern became more and more sharply 

 set apart from each other. Thus it appears that the division of 

 the nebenkern waits upon the final disappearance of the chromo- 

 philic material, the completion of which process signalizes the 

 final splitting of the nebenkern into two parts. 



If there is any real connection between these two phenomena, 

 we should always expect the disappearance of the chromophilic 

 material before the division of the nebenkern. Accordingly, if the 

 absorption of the chromophilic substance is for any reason delayed 

 beyond the initial phases in the drawing out of the nebenkern as 

 a whole, we should expect the nebenkern to elongate as a single 

 mass dividing eventually into two parts at a stage in the elonga- 

 tion dependent upon the time of the disappearance of the chromo- 



