306 The Ecologic Relations of the Photogenic Function among Insects. 



Some interesting speculations as to the phylogenetic relations of 

 the Lampyridae and other luminous insects presents themselves here, but 

 we have so little evidence in any direction that even speculation seenis 

 hardly justified. Olivier (15) has called attention to the main features 

 in the geographic destribution of the Lampyridae. The relatively immense 

 number of species in South America — nearly half of the 1200 described 

 species — is especially interesting and probably significant. The relati- 

 vely scarcity in Africa is also noteworth}^ On the wohle the Lampyridae 

 show the same peciilarities in dispersal as are found among other crea- 

 tures; — e. g., the genus Psilocladus, whose species are found only in 

 South America and in Japan, 



A second interesting group of luminous Coleoptera are the mem- 

 bers of the Elaterid genera Pyrophorus and Photophorus. These two 

 genera are very close, and while little is known as to the habits of 

 Photophorus, it is not improbable that it will prove very much like 

 Pyropliorus. Lund (8) and others have shown that P^rop/iorws is strongly 

 attracted to a moving light, and we are probably safe in assuming that 

 in them the luminous power plays the part of an attraction between 

 the sexes. Photophorus presents one of those remarkable peculiarities of 

 geographic distribution, occurring as it does in the Fiji and nearby is- 

 lands, some eight thousand kilometers from its nearest luminous rela- 

 tives in South America. 



Phengodes has already been referred to under the Lampyridae; 

 the peculiar structures of these insects, the vast differences between the 

 sexes in the adult stage, etc., has long made them a matter of consi- 

 derable entomologic interest; with them Stands, in this regard, Dioptoma 

 adamsii., before referred to. The New Zealand /?o/i'7ojjA//a luminosa seems 

 to be about the best known of the non-coleopterous luminous insects, 

 and presents the only definitely known instance of proven self-lumino- 

 ßity in the entire Order of Diptera. 



Tt it probable that among all the brightly luminous members of 

 the family Lampyridae, the luminosity serves as a means whereby the 

 sexes may meet; it also seems very probable that this is the utility of 

 the photogenic function in all luminous Coleoptera, and indeed in all 

 self-luminous insects. Among others luminous forms, — Annelids, fish, 

 crustaceans, etc., — this may sometimes be the ecologic relation of the 

 function, though in particular instances the defensive and other relations 

 may also enter in. 



1. Barber; Phengodes in the vicinity of Washington, D. C; Proc. Ent. Soc. Wash., 



1906, Vol. 7, pp. 196—197. 



2. Emery; La hice negli amori delle lucciole; Bull. Soc. Entomol. Ital., 1886, 



Vol. 18, p. 406; Stett. Entomol. Zt., 1887, Vol. 48, pp. 201—206. 



3. Galloway; A case of phosphorescence as a mating adaption; School Sei. 



and Math , Decatur, III.. May, 1908. 



4. Galloway and Welch; Studies on a phosphorescent Annelid, üdontosylUs 



enopla Verrill. Trans. Anier. Micros. Soc, 1911. Vol. 30, pp. 13—39. 



5. Gorham; The structure of the Lampyridae with reference to their phospho- 



rescence; Trans. Ent. Soc. Lond., 1880, pp. 63 — 67. 



6. Green; Luminous Coleoptera from Ceylon; Trans. Ent. Soc. Lond., 19r2,j 



pp. 717 — 719. 



7. Lubbock; Origin and metamorphoses of Insects; Lond., 1874, p. 17. 



8. Lund; On light reactions in certain luminous organisms; Johns Hopkins! 



University Circular, 1911, No. 2, pp. 10—13. 



