538 THE POPCLAR SCIENCE MONTHLY 



ners. For instance, the observer would soon notice that the lights of 

 Pliotinus pyralis and Photinus scintillans were decidedly more yellow- 

 ish than those of Photuris pennsylvanica and Lecontea lucifera, and 

 that the latter were distinctly greenish in tone. A little further ob- 

 servation would soon enable one to distinguish these two latter insects 

 from the two former ones also through the different method of light- 

 emission ; the flickering flashes usually given by Photuris and Lecontea 

 differing markedly from the long flash of the Photini. Thus it In- 

 comes probable that different species can recognize their own kind 

 through the color and manner of emission of the light. 



Another interesting circumstance is that the majority of Lam- 

 pyrids have their luminous apparatus on the ventral side, the greater 

 part of the light being directed downwards and sideways, and but very 

 little passing upward. The effect of this ventral arrangement so far 

 as the sexes is concerned is that a female resting on a leaf or on the 

 ground illuminates by her flash a considerable portion of the support- 

 ing surface, and a male flying above her would see not merely a flash, 

 but a silhouette of his mate against an illuminated background. The 

 green color of the light would, of course, be of special advantage on 

 foliage. Moreover, the flash of the flying male would illuminate most 

 particularly an area immediately below him and ahead of him, as these 

 insects fly with the body inclined, the head being highest. In species 

 where the male is non-luminous, or but slightly so, this last service 

 does not exist, while in those like Photuris, where both sexes are about 

 equally active, the manner of applying the luminous property may be 

 entirely different; it is perhaps significant in this latter group, that 

 the light is easily visible from the dorsal side between the elytra. The 

 cucuyo (Pyrophorus noctilucus) in which both sexes are equally active, 

 have lights both above and below. 



We have been considering the purpose of biophotogenicity so far as 

 its application to the creatures possessing the function is concerned, 

 and to a more limited extent, to their enemies. A few words may well 

 be given regarding its relation to man. The use of the cucuyo s as 

 decorations and as night-lamps in the tropical countries is quite well 

 known, and a number of instances have been recorded where travelers 

 have owed their safe passage and even their lives to the light given by a 

 collection of these Elaterid beetles. Several naturalists have written 

 and read by the light of vessels filled with Noctiluca and other sea-or- 

 ganisms, and Chun has photographed a Cephalopod by means of its 

 own light. The luminous bacteria have been put to a number of uses, 

 mainly in the laboratory ; flasks coated on the interior with fresh cul- 

 tures of some of these organisms give light which appears of considerable 

 intensity when the eye becomes accustomed to it, and Dubois and Molisch 

 have taken quite a number of photographs by bacterial light. It has- 



