STUDIES ON INSECT SPERMATOGENESIS. 65 



make one of these types look like the other. This may possibly 

 have occurred with some of the Orthoptera, for I find in my own 

 material of Rhonialcnm, nebenkern figures comparable to those 

 figured by Meves ('oo) in Pygara, and yet Giglio-Tos and Granata 

 ('08) figure in Pamphagus a very clear "spireme." Of even 

 more interest are the old figures of the nebenkern in Gryllus by 

 Baumgartner ('02), in which a "striated condition" very remi- 

 niscent of Gatenby's " spireme " is a conspicuous figure. It is, 

 therefore, by no means improbable that the " spireme " type of 

 nebenkern is more widely distributed than has been suspected. 

 On the other hand I am equally convinced that the " plate-work " 

 type of nebenkern is a reality, and it is scarcely probable that 

 technique of so many kinds (I have tried a great many methods 

 on these Hemiptera (see Bowen ('22))) would fail to reveal a 

 "spireme" in the hemipteran nebenkern if any such structure 

 really existed. The whole series of stages which I have described 

 are hardly to be satisfactorily explained away as artifacts. It is, 

 I think, safe, then, to conclude that there are at least two funda- 

 mental types of nebenkern structure the " spireme " type, and 

 the " plate-work " type possibly interconnected by intermediate 

 conditions ; but until the matter has been carefully examined it 

 will not be possible to classify the various insect groups (other 

 than Lepidoptera and Hemiptera) on the basis of nebenkern 

 type. This whole subject offers an attractive field for intensive 

 study. 



It remains now to follow out the later history of the chromo- 

 philic substance. In the spireme type the chromophilic thread 

 often withdraws from its originally peripheral position, and, after 

 imperfect fixation, the running together of its substance gives 

 rise to the appearances figured by Platner ('89) and Meves ('oo) 

 and already referred to above. The final fate of the spireme is 

 not known in any case. In the Lepidoptera the nebenkern does 

 not divide (according to the current descriptions) as it does in the 

 Hemiptera and many other insects, but merely draws out along 

 the tail filament for which it acts in the role of a mitochondrial 

 sheath. According to Gatenby ('17), as this elongation is going 

 on, "the chromophobe substance 'dwindles,' and the spireme ap- 



