606 ROBERT H. BOWEN 



comparable to those which I have described in Brochymena 

 (Bo wen, 19226). These later stages seem for the most part 

 to have been overlooked by Gatenby — at all events his account 

 of the fate of the chromophilic substance (' spireme ') seems to 

 be entirely incorrect. The source of his statement as to the 

 breakinfT up of the ' spireme ', as shown in his Text-ficr. 3, will 

 be considered in a later paragraph. 



It will be convenient at this point to refer briefly to the 

 parallel course of events in the chromophobic material. As 

 the nebenkern draws out along the axial filament of the 

 tail, both chromo])hilic and chromophobic substances are at 

 first involved (fig. 1). Very soon, however, the chromophilic 

 substance ceases to elongate (figs. 4 and 46), and begins gradually 

 to shorten up as its dissolution advances. The chromophobic 

 material, on the other hand, continues to elongate very 

 rapidly (fig. 8), and tends gradually to become spun out towards 

 both ends ^^^th a median swelling in the region occupied by 

 the remains of the chromophilic plate-work (fig. 46). The 

 proximal end of the nebenkern (not to be made out in fig. 46) 

 seems to be anchored in the vicinity of the insertion of the 

 tail filament, as is the case in other insect sperms. The con- 

 tinued spinning out of the nebenkern results in the production 

 of a mitochondrial sheath for the tail filament, exactly as 

 in the Hemiptera. 



It has long been known that the nebenkern becomes divided 

 into two equal masses in many insect spermatids (Hemiptera 

 and Orthoptera), prior to the spinning-out process, while in 

 Lepidoptera, according to the current descriptions, this divi- 

 sion is entirely omitted. In my study of the nebenkern in 

 Hemiptera (Bowen, 1922 b), I noted for the first time the 

 relation between the final disappearance of the chromophiHc 

 matter and the complete division of the nebenkern into two 

 equal parts. This relation was found to hold true in the Ortho- 

 ptera and Coleoptera also (Bowen, 1922 (?), and I ventured the 

 guess that in the Lepidoptera, ' a division of the nebenkern 

 will be found to occiu- once the chromopliilic substance has 

 been disposed of ' (Bowen, 1922 &, p. 69). This point has been 



