602 ROBERT H. BOWEN 



a mass of soap bubbles. Although Gatenby's figures do not 

 show the point satisfactorily, I have found that in Callo- 

 samia the surface of the nebenkern is often deeply indented 

 at the points where the chromophilic partitions reach its 

 periphery, emphasizing the impression of a vesicular mass. 

 Doncaster and Cannon (1920) also show this very clearly in the 

 nebenkern of the louse (see their figs. 18 and 19). 



In contrasting these two interpretations it must )>e frankly 

 admitted that the appearance of a thread-work is exceedingly 

 deceptive. Indeed, it is possible that neither view can be 

 conclusively proved without taking into consideration the 

 later stages, in which the facts are very clear. Nevertheless 

 two points against the thread-work interpretation may be 

 urged. In the first place, in none of Gatenby's figures or in 

 my own preparation is there any indication of the cut ends 

 of a thread such as are obvious in sections of the chromatin 

 spireme of dividing nuclei. It is exceedingly difficult to under- 

 stand how such loos(^ ends could be constanth' avoided in sec- 

 tions. If, however, the structure of the chromophilic substance 

 is that of a plate- work, the absence of ends is easily 

 explicable. A second objection is based on the optical arrange- 

 ments upon which the demonstration of the chromophilic 

 substance in the spermatocj'te chondriosomes was sho^^•n to 

 depend (see preceding section). It Mill 1)6 clear from a considera- 

 tion of these conditions that the visibility of the chromophilic 

 material in the nebenkern may well depend on its disposition 

 between closely adjacent chromophobic masses, the chromo- 

 philic septa being visible when seen on surfaces of sharp 

 curvature, but invisible when seen in plane view, just as in 

 the case of the individual chondriosome vesicles in the sperma- 

 tocytes. Indeed, every feature of the condensation process 

 becomes readily explicable if we think of it merely as a reduc- 

 tion in the number and arrangement of droplets of chromo- 

 phobic material by the concentration of their chromophilic 

 envelopes into more extensive separating membranes. Such 

 a conception also helps us very much to understand the 

 nature of the same process in other insects — the Hemiptera. 



