PHOTOGENIC ORGANS OF LAMPYRIDS 177 



body elements, from which they may, nevertheless always be distin- 

 guished by their peculiar yellow tint. I have traced the organ which 

 is a definite circumscribed structure, and which I call for the present, 

 the suboesophageal body, through the embryo into the larva, where it 

 disintegrates and finally disappears. I regard it therefore as a truly 

 embryonic and early larval structure, quite distinct, at least physio- 

 logicall}-, from the fat body. Its function is very doubtful. 



He suggests that it may be nephridial. Both the pericardial 

 cells and the suboesophageal body are formed before the fat- 

 body is well differentiated. The pericardial cells are now the 

 largest cells in the body. 



Figure 51 is a cross section through the abdomen of an embryo 

 of about the same age as that illustrated in sagittal section. The 

 ectoderm is quite thick except over the median portion of the 

 ganglion. On each side, closely appressed to the ventral ecto- 

 derm is a subspherical mass of pale cells, the oenocytes, OE. 

 These have been shown by Wheeler ('92) to be of ectodermal 

 origin. At least six such segmental clusters were found in the 

 abdomen of the Photuris embryo. The hypodermis is somewhat 

 thinner where the oenocytes are applied, as if they had been 

 detached at the expense of this epithelium. The oenocytes, 

 compactly massed, with the cell boundaries indistinct, the nuclei 

 dark and reticulated, and the cytoplasm pale and vacuolated, 

 little resemble the large free oenocytes of later life, where, with 

 the exception of the eggs, they become the largest cells of the 

 body. However, they do not surpass the pericardial cells for 

 some time. They become spherical, migrate to the interior 

 with the invaginating tracheae and mingle with some large 

 reticulated fat cells. Oenocytes also occur in the adult beetle 

 where they are often wedged in between the fat-body and have 

 of course lost their segmental arrangement. The gonads, GN, 

 are a compact group of large cells lodged in the splanchnic meso- 

 derm, above and lateral of the paler fat-masses, FB. 



The large arcuate embryo (fig. 41) must reverse its position, 

 i.e., become coiled. The amnion is ruptured in this process. 

 Figures 43 and 44 represent a Photinus embryo, which has 

 become very stout and broad, undergoing this involution. The 

 operation begins at the anterior end, as the caudal portion is 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 1 



