NATURE OF THE LIGHT EMITTED BY FIREFLIES. 45 
genic layer and the so-called “reflecting layer” are penetrated by innumer- 
able trache, which are supposed to be filled with air. During the experi- 
ments recorded herewith, it was found that the fireflies must have access to 
plenty of fresh air to keep them healthy and active. In fact, to the writer it 
appeared that they required more fresh air (oxygen) than would be required 
in the ordinary respiratory processes. Other insects (e. g., several non- 
luminous Elaters) did not seem so sensitive in this respect. 
While it is generally accepted that the light production is connected in 
some manner with an oxidation process, there is no data showing how the 
light emission is brought about. Optically the so-called ‘“‘reflecting layer’’ 
has little if any meaning. Whether it is the storehouse for waste products 
or (what is more plausible) a reservoir containing an oxidizable substance is 
a subject deserving further consideration. As mentioned elsewhere, it 
would be desirable to learn the condition of this layer with the age of the 
insect, and especially after it has flashed for a long time. Since samples of 
Photuris can be obtained which will flash in rapid succession for at least 1 to 
13 hours, it would be interesting to compare its ‘‘reflecting layer” with that 
of a specimen which has not flashed in this manner. But while this may 
give some information in regard to the light production in fireflies, it will 
hardly apply to all organisms. In some organisms the light is developed in 
a less highly organized cell; and, indeed, in the case of some marine animals 
a liquid is ejected which becomes luminous on diffusing in the water. In 
this connection Dubois has already been quoted that the light is produced 
when the ejected liquid passes from a colloidal into a crystalline state. 
Ultimately it may perhaps be shown that the light production is the result 
of energy transformations in passing from the colloidal to the crystalline 
state. In this connection the optical properties of thermo-luminescent fluo- 
rites has been the subject of some study by the writer, but no definite 
results have yet been obtained. Just what happens when fluorite is warmed 
and the thermo-luminescence destroyed is not known. Whether this has 
any bearing on the light emission in animals is difficult to determine. 
WASHINGTON, D. C., September 1, rgrt. 
