June, 1896.] Packard : Phosphorescent Organs of Insects. 65 
veyed to the cells of the luminous body by the tracheae, which branch 
profusely in it and break up into capillaries.” 
Emery states that the males of Luciola display their light in two 
ways. When at night time they are active or flying the light is given 
out at short and regular intervals, causing the well-known - sparkling or 
scintillating light. If we catch a flying Luciola or pull apart one rest¬ 
ing in the day time, or cut off its hind body, it gives out a tolerably 
strong light, though not nearly reaching the intensity of the light-waves 
of the sparkling light. In this case the light is constant, yet we notice, 
especially in the wounded insect, that the phosphorescent plate in its 
whole extent is not luminous, but glows at different places as if phos¬ 
phorescent clouds passed over it. 
It is self-evident that a microscopic observation of the light of the 
glow-worm or fire-fly is not possible, but an animal while giving out its 
light, or a separated abdomen, may readily be placed under the micro¬ 
scope and observed under tolerably high powers. By making the ex¬ 
periment 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, and it is seen that the rings 
of light correspond with the previously described circular tracheal capil¬ 
laries, i. <?., the limits between the tracheal-cell cylinder and the paren- 
chym-cells. The parenchym-cells are never stained of a deep brown ; 
this proves that its plasma may be the seat of the light-producing oxy- 
dation. Hence this process of oxydation 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 oxydized 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 oxydizes 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 defense, or a warning or danger-signal 
