PHYSIOLOGY OF PHOSPHORESCENCE 427 



tone entirely disappears ; on the other hand, the blue strikingly in- 

 creases." As regards the spectrum he found that almost exactly 

 half of the blue end is wanting and that the red part is also a little 

 narrower than in the spectrum of the petroleum flame. 



Professor C. A. Young states that the spectrum given by our com- 

 mon firefly (Photinus ?) is perfectly continuous, without trace of lines 

 either bright or dark. " It extends from a little above Fraunhofer's 

 line C, in the scarlet, to about F in the blue, gradually fading out at 

 the extremities. It is noticeable that precisely this portion of the 

 spectrum is composed of rays which, while they more powerfully than 

 any others affect the organs of vision, produce hardly any thermal 

 or actinic effect. In other words, very little of the energy expended 

 in the flash of the fire is wasted. It is quite different with our arti- 

 ficial methods of illumination. In the case of an ordinary gaslight 

 the best experiments show that not more than one or two per cent 

 of the radiant energy consists of visible rays; the rest is either in- 

 visible heat or actinism ; that is to say, over 98 per cent of the gas is 

 wasted in producing rays that do not help in making objects visible." 



Panceri also remarks that while in the spectroscope the light of 

 some Chaetopteri, Beroe, and Pyrosoma exhibit one broad band like 

 that given by monochromatic light, that of Lampyris and Luciola is 

 polychromatic. (Amer. Nat., vii, 1873, p. 314.) 



The filtered rays of Lampyris pass (like Kontgen and uranium 

 rays) through aluminium (Muraoka). 



The physiology of insect phosphorescence is thus briefly stated by 

 Lang : "The cells of this luminous organ secrete, under the control of 

 the nervous system, a substance which is burnt during the appearance 

 of the light ; this combustion takes place by means of the oxygen con- 

 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 

 resting in the day time, or cut off its hind body, it gives out a toler- 

 ably 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 phospho- 

 rescent plate in its whole extent is not luminous, but glows at differ- 

 ent places as if phosphorescent clouds passed over it. 



It is self-evident that a microscopic observation of the light of the 

 glowworm or firefly is not possible, but an animal while giving out 



