PHOTOGENIC ORGANS OF LAMPYFJDS 161 



The two vertical muscle bundles (M, fig. 26) which partly 

 divide each photogenic organ, persist, with some changes, from 

 the larva to the imago. 



The adult photogenic organs of Photinus have been well de- 

 scribed and illustrated by Townsend ('04), and Lund ('11), and 

 by Geipel ('15) in Europe. 



The larval light-organs begin to deteriorate at least in the 

 pupal stage; the photogenic layer seems to be the first to break 

 up with a disappearance of the nuclei, the layer becoming filled 

 with small black granules or rods. Evidently this is the con- 

 dition of the photogenic organ (fig. 30) in the adult Ellychnia 

 corusca, a lampyrid not held to be luminous in the mature state. 

 Dubois ('98) in speaking of the European Lampyris noctiluca, 

 says, p. 321: "Les organes larvaire persisteront apres la trans- 

 formation de la nymphe, soit en insecte male, soit en insecte 

 femelle; . . . . " 



DEVELOPMENT OF THE LARVAL PHOTOGENIC ORGANS IN 

 PHOTURIS PENNSYLVANICUS 



Owing to the minuteness of this organ, and to the inferior 

 differentiation of the embryonic tissues, the development of the 

 larval light-organs could not be followed with the detail and 

 degree of certitude which the growth of the adult light-organ 

 permitted. It is evident however that as a definite structure, 

 it is formed quite late in the development of the embryo, i.e., 

 when the latter lies in the final curled-up position (fig. 45). It 

 is not improbable that in the earlier stages the light, being 

 diffuse, arises from the yolk granules. Vogel ('13) has made 

 some observations on the development of the photogenic organs 

 in the embryo Lampyris noctiluca. He recognises the fatty 

 origin of the organs, and suggests that the source of luminescence 

 is in the yolk, which in its changes, etc., much resembles the 

 proteid inclusions of the fat-body in old larvae. He studied 

 the light-organs in late embryos (18 days incubation) and states 

 that they do not arise from imaginal discs. 



It is only late in the embryonic development that the two 

 larval lights are discernible through the egg-shell. Long after 



JOURNAL OF MORPHOLOGY, VOL. 28, NO. 1 



