No. 533] PHOTOGENIC ORGANS OF LAMPYR1D2E 311 



chitinous tube, coiled into a nearly cylindrical spiral, 

 represented in partial section by 8, 8, in Fig. 1, a; these 

 two organs appear to be glands which empty into a com- 

 mon duct which could be followed to the posterior ex- 

 tremity, and it seems possible that they are a portion of 

 the male generative system, as they were not found in 

 the female pyralis, although no spermatozoids were 

 seen. The direction of rotation of the spiral was the re- 

 verse on the left side of the insect from that on the right. 

 These organs were not found in the Photuris, although 

 globular, glandular structures were found in approxi- 

 mately the same portion of the latter insect. This struc- 

 ture is shown in Fig. 2 of Miss Townsend's paper on 

 Phot in us marginellus, and in Fig. 1 of Seaman's 

 (Phot huts pi/ nil is) ; the latter erroneously referred to it 

 as the intestine; in our studies, the intestine of both 

 Phot in us and Photuris was seen as a nearly straight, 

 thick-walled tube, indicated in section by / in a and b 

 of Fig. 1. 



The above remarks apply to the male insects. The two 

 sexes in Photuris are almost indistinguishable exter- 

 nally; all those which we sectioned appeared to be males. 

 In Photinus pyralis, however, the female differs mark- 

 edly from the male. The luminous organ in the male 

 occupies the entire ventral surface of the fifth and sixth 

 segments of the abdomen, and the posterior portion of 

 the fourth segment. In the female, the luminous appa- 

 ratus is visible externally as a small, rectangular yellow 

 spot, occupying about one third of the ventral area of 

 the fifth segment of the abdomen. This organ obtains its 

 air supply from a large trachea which extends along its 

 forward edge, and apparently connects with the spiracles 

 on the dorsal edges of the segment. In its finer struc- 

 ture, the photogenic organ of the female pyralis appears 

 to be exactly like that of the male, as is to be expected. 



That the photogenic process is an oxidation is scarcely 

 to be doubted, in view of the work which has been done 

 already. The work of one of us (McD.) with Professor 



