306 ENTOMOLOGICAL NEWS. [July, ' J 7 



Unaware of Williams' work, which did not appear until 

 late December, the writer had undertaken a study of the 

 embryonic development of the photogenic organs of Photuris 

 pennsylvanica. This work was at the suggestion of Dr. W. 

 A. Riley, to whom the writer is indebted for helpful advice 

 and criticism in the completion of this paper. On the basis 

 of this work he is forced to conclude that neither Vogel not 

 Williams studied the organ in its earliest development, and 

 that they drew mistaken conclusions from observations of 

 organs already developed beyond the critical stage. 



Material for study was obtained by confining the adult in- 

 sects in small jars that were partly filled with earth and moss. 

 Since oviposition occurred very readily in captivity, it was 

 easy to obtain a complete series of eggs by removing the in- 

 sects to different jars each day. During the summer of 1916 

 the eggs of this species hatched in from 25 to 27 days, depend- 

 ing on temperature, with an average of 26 days. Eggs were 

 killed in hot water, dehydrated and imbedded in paraffin. 

 Sections were cut three and four microns thick. As it was 

 often difficult to find the eighth abdominal segment, sagittal 

 sections were by far the most satisfactory. Heidenhain's 

 iron haematoxylin was very satisfactory for staining. Various 

 other stains were tried with less success. Eosin was some- 

 times used as a counter stain. 



It was found in the 14-day embryos, that the hypodermis 

 on the ventro-lateral portion of each side of the eighth ab- 

 dominal segment, in its anterior region, showed a definite 

 thickening, due to proliferation and enlargement of the cells, 

 as shown in Fig. I, (H). The nuclei of the cells were also 

 larger than those of other hypodermal regions. 



In the 15-day embryos the organ appeared as a distinct 

 nodule which projected from the inner surface of the hypo- 

 dermis (Fig. 2, P). At this stage there was no evidence of 

 any separation from the hypodermis. In fact the hypoder- 

 mal cells extended up slightly between the cells of the nodule 

 itself. 



By studying a large number of embryos it was definitely 



