162 F. X. WILLIAMS 



the oenocytes, whose compact and appressed segmental clusters 

 {OE, fig. 51) much suggest light-organs, have migrated from the 

 body wall into the body cavity, and the fat-body and haemo- 

 cytes have become differentiated, but before the cuticula and 

 hairs have appeared, the photogenic organ (0, fig. 15) is discern- 

 ible as a compact mass of rather large, distinct and well-nucleated 

 cells, lying on each side in the eighth abdominal segment, between 

 the anterior end of the segment and its tracheal invagination. 

 The organ is closely applied to the hypodermis, but is neverthe- 

 less distinct, though the hypodermis is quite thin where it is in 

 contact with the organ. This fact might suggest that the hypo- 

 dermis gave rise to the light-organ, but the former is of variable 

 thickness and its cells are quite unlike the nearest cells in the 

 light-organ. These moreover, do not appear to be the youngest 

 cells, as should be the case were they of hypodermal origin, as 

 Dubois affirms of Lampyris noctiluca. On the other hand, the 

 inner cells, i.e., those nearest the fat-body, which appears almost 

 as a syncytial mass, greatly resemble those fat cells (A, fig. 15) 

 with which they are in contact. They are more vacuolated here 

 and this suggests their fatty • origin. The whole cell-mass is 

 approximately spherical and measures about 17 by 21 micra. 

 The cells for the most part are already differentiated from the 

 fat-body, as their protoplasm is denser and contains small yellow- 

 ish-brown granules. The cells are also smaller in size. No 

 tracheae as yet penetrate the organ, nor could nerves be found 

 in connection with it. A large cylinder of tracheal epithelium 

 T, is near, but has as yet secreted very little or no chitin. The 

 stage of development above described could be found in but a 

 single specimen. The cells indicated a spiral arrangement and 

 gave no indication of the two layers. No blue-staining proteids 

 occurred either in the fat cells or in the light-organ; the yolk 

 mass probably furnished much of the food material. 



A considerably later stage of development (fig. 14) is to be 

 found in the well-chitinized larva, with hair, spines and appen- 

 dages completely or nearly completely developed. Such larvae 

 are capable of moving within the egg-shell, and their photogenic 

 organs appear through the latter as two points of light. The 



