404 THE CANADIAN ENTOMOLOGIST. 



about equally active, and powerful flyers; the male has slightly the larger 

 luminous apparatus of the two, and somewhat larger eyes. No connection 

 between the different modes of light-emission of this species and the two 

 sexes could be made out. 



Two random observations : Those males o( Fhothius pyralis which 

 seemed strongest and most active, were frequently noticed to have the 

 ventral surface of the luminous segments of a pale salmon-pink colour, 

 instead of the usual sulphur-yellow ; the assumption is that these were 

 newly-emerged insects, and that this salmon-pink is the initial colour 

 of the photogenic organ, and that after use the usual sulphur-yellow colour 

 appears. The colour of the light appears to be exactly like that of the 

 insects with the yellow surfaces to these segments. Whether this change 

 denotes a using-up of the photogenic material is an interesting problem, 

 but one that would be difficult to solve. Second : One specimen of 

 Phot 'urns sciniillaiis ? was observed in which the rudimentary elytra were 

 at least one-half longer, proportionately, than is usual in this insect, per- 

 haps representing a tendency to a dimorphic female in this species. 



It may be objected that the proof submitted here is not sufficiently 

 convincing as to the primarily sexual relation of the photogenic function. 

 Perhaps it is not ; there are various hypothetical questions that might be 

 raised regarding it. But the writer believes that if anyone will take the 

 trouble to observe some of these three species, or any of their near rela- 

 tives, they will doubtless come to the same ultimate conclusion — that the 

 light, as actually used by the insects, is primarily for the purpose of sexual 

 attraction, and that the reproduction and continuance of the species de- 

 pends upon it. 



A brief review of what literature there is on this subject maybe of 

 some interest here. 



There has been considerable difference of opinion in times past as to 

 the precise purpose of the luminosity of the Lampyrid^e, some holding it 

 to be a secondary sexual character, others claiming that it is purely defen- 

 sive in nature, and still others declaring that neither of these explanations 

 satisfied the conditions, and that the luminosity plays some part in the life 

 of the insects of which we had no knowledge. There seems to have been 

 really surprizingly little actual observation one way or the other. A diligent 

 search- of the references given in the "Zoological Record" since its founda- 

 tion yielded but few papers dealing with this question — itself obviously 

 one of fundamental biologic importance — and those found for the most 



