608 ROBERT H. BOWEN 



groove between the two halves of the divided nebenkern, just 

 as in other insects. 



After the division of tlie neljenkern (probably) the chromo- 

 phobic material bc^gins to develop constrictions, at first in the 

 more distal region of the sheaths, which (hvide it into a series 

 of bead-like masses. This process is shown particularly well in 

 figs. 7 and 10, although the development of these bleb-Uke 

 swellings is often (usually ?) deferred until after the disappear- 

 ance of the chromophilic material. The last -mentioned figure 

 is from a cyst of abnormally large sperms, and this may 

 account for the unusually earh^ development of the swellings. 

 These bead-like masses are rapidly separated from each other 

 by the spinning out of the intervening chromophobic material. 

 As a rule these delicate connecting strands are not well seen, 

 and the tails look like a series of clear vesicles often ^^^thout any 

 apparent connectives (fig. 11). This is particularly true in the 

 later stages of sperm formation, w-hen (he vesicles seem merely to 

 be scattered loose along the tail filament (figs. 17, 25, 35, 37, 40, 

 and 52 for instance). However, in material fixed in Flemming 

 without acetic acid and strongly stained in Fe-haematoxylin 

 the chromophobic material can sometimes be coloured very 

 sharply, and it is possible in favourable cysts to make out the 

 actual structure of the nebenkern derivatives \vith the greatest 

 clearness. From such preparations it is evident that the original 

 halves of the nebenkern have become spun out into delicate 

 threads which run parallel to the tail filament and at intervals 

 bear the bleb-like swellings, now present in larger number 

 but individually much reduced in size. The general appear- 

 ance is exactly like that in Euschistut* (see Bowen, 1922 &, 

 fig. 27). It is clear that these swellings are homologous with 

 the ' tail vesicles ', the formation of which was described fully 

 in the Hemiptera (Bowen, 19226). 



Finally, the central substance which I have described 

 in detail in the Hemiptera (Bowen, 1922 b), and less com- 

 pletely in Orthoptera (Bowen, 1922<?), remains to be con- 

 sidered. As in the Hemiptera this material first becomes visible 

 in the chromophobic area of the nebenkern during the middle 



