INSECT SPERMATOGENESIS 609 



Stages in the dissolution of the chromophihc substance (figs. 4, 

 5, and 6). It does not stain very sharply with Fe-haematoxylin 

 and its exact morphology is difficult to make out. It seems, 

 however, to consist of small droplets which tend to run together 

 to form more or less irregular threads traversing the chromo- 

 phobic material in a direction parallel to the long axis of the 

 nebenkern (fig. 7, 8, and 13). As the chromophilic material 

 disappears, the central substance becomes more conspicuous 

 (fig. 10), and in cross-sections of the nebenkern appears exactly 

 as it does in the Hemiptera (figs. 9 c and 12b). In fig. 47 b 

 it has become condensed into a single strand in each half of the 

 nebenkern. (Compare with Holmgren's (1902) account in 

 Silpha, fig. 9 m.) As, in Ceuthophilus (Bowen, 1922^), 

 the central substance is present in the tail vesicles in much the 

 same form in which it appears in the unconstricted nebenkern 

 (figs. 10, 11, and 48). A more detailed account of the central 

 substance may be omitted here, since I have discussed the 

 subject in another paper (Bowen, 19226), to which the reader 

 is referred for comparative details, especially in the Hemiptera. 



It will be observed that Gatenby has failed to recognize 

 the central substance in the lepidopteran nebenkern. In 

 studying his figures I have come to the conclusion that the 

 thread-like formations shown in the nebenkern in his figs. 47 

 and 20 are to be interpreted as central substance. He describes 

 these threads as resulting from the breakdown of the ' spireme ', 

 a conclusion which he seems to have reached on the basis of 

 the supposed structure of the early nebenkern, without having 

 traced out the necessary connecting hnks between the two. 

 My observations leave no doubt that the chromophilic and 

 central substances are morphologically distinct, and that 

 whatever the structure of the chromophilic material may be, 

 that of the central substance is in no way dependent upon it. 



So far as my observations go they indicate that the threads, 

 spun out from the halves of the nebenkern, ultimately form 

 a sheath for the tail filament of the mature sperm, as described 

 in other insects by various workers. The fate of the tail vesicles 

 is not known. 



