PHOTOGENIC ORGANS OF LAMPYRIDS 179 



proportionally shorter. The cells are four to six times as long 

 as wide and form a flat disc. The nuclei occupy an approxi- 

 mately central position in the cells which may already be vacuo- 

 lated just below the nuclei, but elsewhere well filled with a granu- 

 lar secretion which largely obscures the cell boundaries. The 

 thin capping membrane is here frequently separated from the 

 apices of the cells. Fat cells largely occupy the base of the 

 peduncle. 



A later stage, such as occurs in larvae nearly ready to hatch 

 (figs. 45 and 55), shows that the gland has already largely per- 

 formed its function. The cap C, may be depressed, irregular or 

 wavy, the gland cells, G, now well below and separated from the 

 cap, form a concave disc or crater, and seem almost to have 

 exhausted the secretion, for very little of it is in evidence. The 

 now spherical or subspherical nuclei, of the same height in each 

 cell, strongly augment the crater-like appearance of the layer. 

 Each cell has the walls closely applied to those of its neighbors, 

 but the dividing line, B, between is usually discernible. Extend- 

 ing from just above the nucleus is the large conspicuous gland 

 duct, D, flaring somewhat distally and often saccate at the base, 

 so that the whole glandular structure, distally, has a papillose 

 aspect. The basal portion of each cell, i.e., immediately below 

 the nucleus, is marked by a large space or vacuole, V, beyond 

 which are smaller indefinite vacuoles and protoplasmic strands. 

 No muscle was found to connect with the organ, and in but one 

 case what seemed to be a duct, leading from the distal portion 

 of the gland into the body cavity, could be made out. The 

 unmodified hypodermis, H, extends well up the sides of the cup 

 where it passes off rather abruptly into the outer gland-cells. 

 Viewed from above, the tips of the gland-cells form a network, 

 the ducts constituting the circular or subangular spaces, the 

 meshes, the cell walls. 



It is quite evident that these large gland-cells are hypodermal 

 and modified by elongation, etc. and from the jointed appen- 

 dage, which, at first bilaterally symmetrical, becomes per- 

 fectly radial and extends somewhat pleurally of the thoracic 

 appendages. 



