The Ecologic Relations of the Photogenic Function among Insects. 303 



The Ecologic Relations of the Photogenic Function among 



Insects. 

 Von F. Alex McDermott, Pittsburg, Pa. 



Among the noumerous iuteresting problems connected with the 

 emmission of light by living organisnis are those which center around 

 the usefulness of the light-producing power to the organisms theinselves. 

 For the great majority of luminoiis creatures no definite conclusions 

 as to the utility of the luminosity can be reached, although there are 

 good reasons for considering that it is probably defensive, alluring etc., 

 in function, in various groups. 



In at least two phyla, howewer, it has been possible to arive at 

 a definite explanation of the usefulness of the photogenic function during 

 the life of the organisms: 



Among the Annelids, Galloway 1,3) and Galloway and Welch 

 (4) have shown that the luminosity serves as a mating adaptation in 

 Odontosyllis enopla. Recently Potts (17) has called attention to the 

 similar habits of Odontosyllis phosphorea, in which the luminosity 

 appears to play a more subordinate part in mating. Lund (8) has also 

 niade observations on marine annelids. 



It is among the insects, however, that we have the most definite 

 cases of the application of the light-producing power to lives of the 

 organisms. Among the Coleoptera there is the family Lampyridae, in 

 which a very large number of the species possess the photogenic function. 

 The surmises as to the usefulness of this function to these insects have 

 embraced the protective, alluring and reproductive ideas, but it is now 

 known that in at least certain of the genera of Lampyrids, the photo- 

 genic function serves, as in the Odontosyllids mentioned above, as a 

 mating adaptation. Among the older writers, Spallanzani (18) and 

 Rennie (19) both called attention to the attraction between the sexes 

 apparently as the result of the luminosity, though the latter writer is 

 inclined to interpret his observations as rather opposing the theory of 

 the significance of the function for mating. Lubbock (7) notes a si- 

 milar instance. 



The first conclusive observations were made by Osten-Sacken (16)^ 

 on the American species Photinus pyralis. Osten-Sacken found that 

 the females of this species remained clinging to grass, leaves, etc., while 

 the males flew above them, flashing at intervals. When the flash of a 

 male was seen by a female, she answered by flashing, and upon the 

 male seeing this answering flash, he alighted near the female, finally 

 locating her definitely through subsequent flashes, and mating with her. 



Next chronologically were the observations of Emery (2) upon 

 Luciola Ualia. Emery watched the actions of the sexes in this species,. 

 and concluded that they depended upon the use of the luminous power 

 for meeting and mating. He then tried a number of experiments, and 

 found that females enclosed in a perforated opake box did not attract 

 males, while those enclosed in glass vials did, thus excluding the effect 

 of odors. 



Osten-Sacke n's paper was not well known until recently, and 

 his observations were accordingly fequently overlooked, he records, ho- 

 wever, what is probably the first definite establishment of the ecologic 

 relations of the photogenic function in any species. Not knowing of 



