358 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1911. 



originated, and why ? The phylogenetic problems are certainly very 

 interesting, and present remarkable instances of "convergence." It 

 is hoped to collect some of these cases and develop them in a future 

 paper. 



5. FLUORESCENT SUBSTANCES IN LUMINOUS INSECTS. 



An interesting circumstance in this connection is the existence in 

 certain luminous organisms of a substance whose solutions exhibit a 

 brilliant blue fluorescence. Dubois ( 12 - 14 ) found this substance in 

 the cucuyo, and in Luciola italica, and named it "Pyrophorine," from 

 Pyrophorus noctilucus, the entomologic name of the cucuyo. More 

 recently Coblentz ( 4 ) has found it in Photinus pyralis, Photinus cor- 

 rusus, and Photuris pennsylvanica, and the author has found it in 

 Photinus consanguineus, P. scintillans, and Lecontea lucifera. It is 

 also present in the larva of Photinus pyralis, and in other lampyrid 

 larvse. Dubois ( 12 - 14 > iy ) regarded this substance as a glucoside, 

 analogous to esculin (a glucoside which is present in the bark of the 

 horse-chestnut, and whose solutions possess a blue fluorescence), 

 while the present author ( 47 ) concluded that it had an alkaloidal 

 nature, and not at the time being aware that Dubois had offered the 

 name "Pyrophorine" for the fluorescent material from -the cucuyo, 

 suggested the name "Luciferesceine" for the substance from the 

 Lampyridae. Neither view as to its chemical nature is at all definite, 

 however, and more work will be necessary to elucidate this point. 



Fluorescent extracts of the pyralis are produced by extraction with 

 alcohol, ether and water, but not by chloroform, benzene, or carbon 

 tetrachloride. The fluorescent material is not precipitated by lead 

 acetate, mercuric chloride, ammonium sulphate, nor chlorplatinic 

 acid. It appears to be a solid at ordinary temperatures, though as 

 emitted by the insect it is contained in a sticky exudation, which 

 soon hardens in the air. 



Luciferesceine dissolves readily in liquid ammonia, the solution 

 presenting the blue fluorescence characteristic of aqueous and alco- 

 holic solutions, the solution itself being very pale yellow. 



Dubois seems to have regarded this substance as of use to the 

 insect in transforming useless into visible radiation, and thus improv- 

 ing the quality or intensity of the emitted light ; and he states that on 

 this theory he first advanced the idea of the use of fluorescent mate- 

 rials with artificial illuminants to improve the quality of the light, 

 as is now done in the use of rhodamine with the mercury vapor arc. 

 Two things, however, stand in the way of the acceptance of the view 

 that the fluorescent property of this substance is of use to the insect; 

 first, the internal juices of the insects (at least of Photinus pyralis) 

 are slightly but distinctly acid, and it has been found that even a 

 weak acid reaction destroys the fluorescence; second, Ives and Co- 



