PHOTOGENIC ORGANS OF LAMPYRIDS 155 



As the fat cells become more and more expelled, the invest- 

 ment thickens and the number of fat haemocytes often increases 

 to such an extent that in their crowded condition they become 

 noticeably squeezed and attenuated, and form a mass several 

 rows deep (fig. 18), the outer haemocytes being more rounded, 

 the inner closely applied, in a roughly radial fashion to the 

 investment. They frequently contain fine yellowish granules, 

 such as occur in the fat and also constitute the blood plasma. 



The ultimate fate of the investment and what may remain of 

 the fat-body within was not definitely ascertained. I often 

 found in sagittal sections through the thorax of pupating larvae, 

 groups of much reduced investments (/, fig. 19) circular or 

 U-shape in outline, according to the section, and sometimes 

 containing a network of cytoplasm or a few proteid granules 

 and what seemed to be waste matter. Such investments were 

 still at least partially surrounded by the much vacuolated fat 

 haemocytes whose irregular outlines and frequently attenuated 

 and eccentric nuclei would seem to indicate a degenerating 

 condition. It appears probable that the investments disappear 

 before the adult condition is reached. They were not well 

 defined in the less studied Photuris larvae. 



The photogenic fat cells which are set free in this manner 

 are large. Their nuclei soon round up considerably. They still 

 contain the large blue-staining proteid bodies so conspicuous in 

 the fat-body proper. The cells (P, fig. 25), as yet undifferen- 

 tiated, migrate to the body wall and apply themselves to the 

 hypodermis, H, where they form an uneven layer. Even at 

 this early stage of development in pupating larvae, some of the 

 tracheal branches, arising from the large stigmatic stem invagi- 

 nated from segments six and seven, push through the photogenic 

 tissue, even to the hypodermis. But the tracheae in the photo- 

 genic tissue are not yet differentiated, for they resemble those 

 in other portions of the body {T. figs. 24, 25 and 27). In a later 

 stage (fig. 27), it is three or more cells deep, and, though the 

 mass is still rather indefinite, it begins to show a differentiation 

 into two layers. The cells have become denser, containing as 

 they do rather sparse little pale yellow granules and a fine net- 



