604 ROBERT H. BOWEN 



In th(' larger spermatids of C a 1 1 o s a m i a , the general appear- 

 ance is still exceedingly complex, perhaps justifying the repre- 

 sentation which Gatenby gives in his figs. 40 and 42, for example. 

 But in the smaller spermatids, where the chromophilic material 

 is much less extensive, the condensation early reaches a point 

 wliere arrangements are sufficiently simple for a practically 

 complete analysis. Such a small spermatid of Callosamia 

 is shown in fig. 44. The chromophilic material occupies the 

 central area of the nebenkern, enclosed in a cortical zone of 

 chromophobic substance, and arranged in the familiar ' onion ' 

 pattern which has been repeatedly figured by many workers 

 on insect sperm formation. (Compare my figures from the 

 Hemiptera (Bowen, 1922b).) 



The further condensation of the chromophilic material 

 now goes on rapidly, in a manner very similar to that which 

 1 have described in Hemiptera. In the Lepidoptera, however, 

 the nebenkern begins to elongate soon after the cortical 

 chromophobic area is established, this area remaining, in the 

 immediately subsequent stages, as a characteristic feature of 

 the nebenkern structure. With the elongation of the nebenkern 

 the condensation of the chromophilic material has soon pro- 

 gressed to a point where the details of its arrangement become 

 sufficiently simplified for satisfactory analysis. I have studied 

 these later stages in both Callosamia and Pygaera, 

 the latter being particularly good on account of the large size 

 of the spermatids. An early stage in the elongation of the 

 nebenkern of Pygaera is sho\m in fig. 1, and in fig. 3 a cross- 

 section through a nebenkern of the same stage. Figs. 4 and 5 

 are similar views at a slightly later stage in the elongation, 

 and fig. 6 is a cross-section of the nebenkern in a still older 

 spermatid. In fig. 45 is showii a cross-section of a nebenkern 

 in Callosamia when its elongation is well begun, and fig. 46 

 is a total view of a spermatid at a stage intermediate between 

 that of figs. 4 and 8. Figs. 8, 10, 14, and 13 are progressively 

 later steps in the condensation of the chromophilic sub- 

 stance. 



A comparative study of this series of longitudinal and cross- 



