428 TEXT-BOOK OF ENTOMOLOGY 



its light, or a separated abdomen, may readily be placed under the 

 microscope and observed under tolerably high powers. By making 

 the experiment in a rather dark room Emery saw clear shining rings 

 on a dark background. " All the rings are not equally lighted. 

 Comparing this with the results of anatomical investigation, it 

 is seen that the rings of light correspond with the previously de- 

 scribed circular tracheal capillaries, i.e. the limits between the 

 tracheal-cell cylinder and the parenchym-cells. The parenchym- 

 cells are never stained of a deep brown ; this proves that its plasma 

 may be the seat of the light-producing oxidation. Hence this pro- 

 cess of oxidation takes place in the upper surface of the parenchym- 

 cells, but outside of their own substance. The parenchym-cells in 

 reality secrete the luminous matter; this is taken up by the tracheal 

 end-cells and burnt or oxidized by means of the oxygen present in 

 the tracheal capillaries. Such a combustion can only take place 

 when the chitinous membrane of the tracheae is extraordinarily fine 

 and easily penetrable, as is the case in the capillaries of the photo- 

 genic plate ; therefore the plasma of the tracheal cells only oxidizes 

 at the forking of the terminal tracheal twigs and in the capillaries." 

 (Emery.) 



The color of the light of Luciola is identical in the two sexes, and 

 the intensity is much the same, though that of the female is more re- 

 stricted. The rhythm of the flashes of light given out by the male 

 is more rapid, and the flashes briefer, while those of the female are 

 longer, more tremulous, and appear at longer intervals. 



Emery then asks : What is the use of this luminosity ? Is it only 

 to allure the females of Luciola, which are so much rarer than the 

 males ? Contrary to the general view that it is an alluring act, he 

 thinks that phosphorescence is a means of defence, or a warning or 

 danger-signal against insectivorous nocturnal animals. If we dissect 

 or crush a Luciola, it gives out a disagreeable cabbage-like smell, and 

 perhaps this is sufficient to render it inedible to bats or other noc- 

 turnal animals. An acrid taste they certainly do not possess. 



It has long been known that the eggs of fireflies, both Lampyridae 

 and Pyrophorus, are luminous. Both Newport and more recently 

 \Viclo\vicjski attributes the luminosity not to the contents of the 

 egg, but to the portions of the fat-body cells or fluid covering on the 

 outside of the eggs, due to ruptures of the parts within the body of 

 the female during oviposition. The larvae at different ages are also 

 luminous. 



The position of the luminous organs changes with age. In the 

 larvae of Pyrophorus before moulting, according to Dubois, the lumi- 



