THE CANADIAN ENTOMOLOGIST 363 



been suspected. Since observing this instance, several similar, but not so 

 clearly defined cases, have been noticed. Barber's observations on Phen- 

 godes /aiicoilis {?i:oc.\Nsis\\. Ent. Soc.,Vol. 7, pp. 196-197), also point strong- 

 ly to the relation between luminosity and sexual function in that species.* 



Both sexes oi pyralis appear to be non-luminous during copulation, 

 but flash if disturbed. 



The phenomenon would be easier to understand if only the apterous 

 or more sluggish females were brightly luminous, while the males, as in 

 P/iengodes laticoilis, were non-luminous, or but slightly so. But in our 

 two species most common here the male is either considerably brighter 

 than the female or approximately equal to his mate in brilliancy. The 

 luminosity of larvae is also a litde hard to comprehend, except as a 

 developmental form of a rudimentary organ. Dubois has claimed that 

 even the unfertilized eggs are luminous. 



That tlie light has also a protective function is also readily surmised. 

 I have heard of at least one bona fide instance, where the sudden flash of 

 a fire-fly saved him from being made a portion of the evening meal of a 

 chicken. Between the li^ht which they give and the sticky exudation and 

 unpleasant odour of most sjiecies, it seems hardly likely that they would 

 prove a tempting morsel to insectivorous creatures. Toads, it is said, 

 have been known to eat them. 



There seems to have been some discussion, in times past, as to 

 whether the light-emission of the various luminous forms was voluntary, or 

 at least under the control of the organism. One argument that was 

 advanced against the view that the phenomenon was under the control of 

 the organism was that the light of the luminous tropical elaters, cucuyo, 

 etc., was constant, and not intermittent. Anyone who studies the natural 

 light-emission of the Lampyridae can scarcely help but conclude that, 

 except when they are subjected to some powerful excitement, such as 

 mechanical, electrical or chemical stimuli external to the organism, the 

 light-emission is entirely voluntary, and under the control of the will. 

 Apparently the insects of the group Luciola emit a continuous twinkling, 

 which has been stated to be synclironous with the respiratory movements 

 of the abdomen, or with the circulatory impulses of the hemolymph ; such 

 synchronism may exist, but it would hardly seem to be proof that the light- 

 emission was not under the control of the insect's will. The cucuyo, indeed, 

 has been observed to vary the intensity of its light apparently entirely at will. 



*I regret that in tliis connection I have not yet been able to secure a recent 

 paper by Meissner, "Wie leuctiten die Lampyrida;?" in the Entomologische 

 Wochenblatt, 1907, V^ol. 24, p. 61. 



