BIOLOGY OF LIGHT PRODUCTION — MALUF 379 



The organs are equally developed in both sexes and luminesce all 

 the year round and not only, as some have believed, during the breed- 

 ing season (Cook, 1900). The fact that all the Geophilidae are eyeless 

 also indicates that luminescence in these forms does not serve for sex 

 attraction. Light production may, however, conceivably be signifi- 

 cant in repelling enemies or in attracting prey. 



It is of phylogenetic interest to note that the luminosity of certain 

 "terrestrial" oligochaete annelids (Walter, 1909) is produced by the 

 secretion of hypodermal glands. 



8. Heiapoda. — Luminous insects are nearly restricted to two 

 families of the Coleoptera: (1) The Elateridae or "fireflies," 3 have 

 many luminous species all of which belong to the nonarid tropics or 

 subtropics and all of which are members of the genus Pyrophorus. (2) 

 The Lampyridae or "glow-worms," contain several hundred known 

 luminous species, included in several genera, most of which occur in 

 America, the West Indies, and the Malay Archipelago. In many 

 species both sexes may be about equally luminous while in others the 

 intensity of light production may predominate either in the female or 

 in the male but more usually in the latter. 



The luminous organ of at least a number of Lampyridae probably 

 arises from the same embryonic fundament as the fat-body (cf. Wil- 

 liams, 1916-17, and Okada, 1935) and lies above the sixth and seventh 

 abdominal sterna. It consists of (1) a dorsal layer of reflector cells 

 which are white in appearance owing to the presence of crystals of 

 xanthin, uric acid, or both; (2) a ventral mass of large cells (the light- 

 producing cells) containing photogenic granules (not fat granules); 

 (3) large tracheal trunks and tracheoles; (4) nerve fibers; (5) nonpig- 

 mented and somewhat translucent sternal plates beneath the light- 

 producing cells. Pyrophorus (an elaterid) has a pair of light-organs 

 at the lateral tergal margins of the prothorax and also a single light- 

 organ on the ventral anterior median region of the abdomen. 



In the larva of the tipulid fly, Bolitophila luminosa (Wheeler and 

 Williams, 1915), part of each Malpighian tubule is photogenic. This 

 is an interesting modification when one realizes that the essential 

 feature of the reflector layer is insoluble purine crystals. Insects with 

 luminescent organs also occur among the Collembola (Lipura, Am- 

 phorura, Neanura), the Neuroptera (Teleganoides, Coenis), and the 

 Diptera (Bolitophila and Ceroplatus larvae). Certain Collembola 

 (Heidt, 1936) secrete a luminous fluid to the exterior, the lumines- 

 cence of which was shown not to be due to bacteria. 



The interior of certain "firefly" eggs (Pyrophorus and various 

 lampyrids) luminesces even prior to any embryonic differentiation. 

 Dubois (1885) observed this to be the cause of error of some observers 



» A "firefly" is any luminous beetle capable of flight, elaterid or lampyrid. A "glow-worm" is any prac- 

 tically wingless luminous beetle, larva, or adult. 



