426 TEXT-BOOK OF ENTOMOLOGY 



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

 maim shows that, as in the Lampyridae, it consists of distinct cells, 

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

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

 Brazilian Pyrophorus Wielowiejski shows that the phosphorescent 

 plate consists of two layers, the upper usually being rilled with crys- 

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

 consisting of distinct polygonal cells, among which are numerous 

 tracheal stems, with taenidia, coursing in different directions, when 

 freshly filled with air, and sending capillaries into the underlying 

 photogenic layer. The latter shows in its structure a striking dif- 

 ference in the cellular arrangement from that of Lampyrids. In the 

 upper or non-photogenic layer are tracheal capillaries which pass 

 down into the underlying cellular plate and which are in the closest 

 possible relations with the single cells a point overlooked by Heine- 

 mann. 



Physiology of the phosphorescence. As is well known, the phos- 

 phorescence of animals is a scintillating or glowing light emitted by 

 various forms, the greenish light or luminous appearance thus pro- 

 duced being photogenic, i.e. without sensible 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 spec- 

 trum. " Langley has shown that while only 2.4 per cent of lumi- 

 nous 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 of the 

 sun, the radiation of the firefly (Pyrophorus noctilucus) consists 

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



The spectrum of the light of the cucujo was found by Pasteur to 

 be continuous. (C. E. French Acad. Sc. 1864, ii, p. 509.) A later 

 examination by Aubert and Dubois showed that the spectrum of the 

 light examined by the spectroscope is very beautiful, but destitute 

 of dark bands. When, however, the intensity diminishes, the red 

 and orange disappear, and the green and yellow only remain. 



Heinemann studied the cucujo at Vera Cruz, Mexico. At night in 

 a dark room it radiates a pale green light which shows a blue tone to 

 the exclusion of any other light. The more gas or lamp light there 

 is present, the more apparent becomes the yellowish green hue, which 

 in clear daylight changes to an almost pure very light yellow with a 

 very slight mixture of green. " In the morning and evening twi- 

 light, more constantly and clearly in the former, the cucujo light, at 

 least to my eyes, is an intensely brilliant yellow with a slight mixt- 

 ure of red. In a dark room lighted with a sodium light the yellow 



