June, 1896 ] Packard : Phosphorescent Organs of Insects. 63 



the cell plasma appearing to be dissolved, the cells having lost their 

 cohesion. 



In comparing the phosphorescent plate or organ of Liiciola with 

 that of Lampyris, the general structure, including the clear cell ele- 

 ments of the cylindrical lobules, which envelop the perpendicular tra- 

 cheal twigs and their branches, and also the granular parenchymatous cells 

 are alike in both, though the arrangement and distribution of the ele- 

 ments in Luciola is more regular^ in Lampyris the tracheal stems being 

 irregularly scattered through the parenchym. 



Wielowiejsky found in the larval and female Lampyris a higher 

 degree of differentiation than in the male, and Luciola has a more dif- 

 ferentiated photogenic organ than Lampyris, as seen in the more regu- 

 lar structure of the lobules. 



As regards the light apparatus of Pyrophorus, or the cucujo, 

 Heinemann shows and that as in the Lampyrid^e, it consists of distinct cells 

 may be regarded as a glandular structure. It is rich in tracheae and 

 the other parts already described. In still later researches on a Bra- 

 zilian Pyrophorus Wielowiejsky shows that the phosphorescent plate 

 consists of two layers, the upper usually being filled with crystalline 

 urate concretions, and entirely like those of the Lampyridse, consisting 

 of distinct polygonal cells, among which are numerous tracheal stems, 

 with taenidia, and coursing in different directions, when freshly filled 

 w'ith air, and sending capillaries into the underlying photogenic layer. 

 The latter shows in its structure a striking difference in the cellular ar- 

 rangement from that of Lampyrids. In the upper or non-photogenic 

 layer are tracheal capillaries which pass down into the underlying cellu- 

 lar plate and which are in the closest possible relations with the single 

 cells, a point overlooked by Heinemann. 



Physiology of the Phosphorescence. 



As is well known, the phosphorescence of animals is a scintillating 

 or glowing light emitted by various forms, the greenish light or lumi- 

 nous appearance thus produced being photogenic, /. <?., without sensi- 

 ble heat. 



Langley rates the light of the firefly at an efficiency of 100 per 

 cent., all its radiations lying within the limits of the visible spectrum. 

 " Langley has shown that while only 2.4 per cent, of luminous waves 

 are contained in the radiation of a gas-flame, only 10 per cent, in that 

 of the electric arc, and only 35 per cent, in that ot the sun, the radia- 

 tion of the fire-fly {Pyrophorus noctilucus^ consists wholly of visible 

 wave-frequencies." (Barker's Physics, p. 385.) 



