METAZOA INSECTA . 435 



carrion which the adults (No. 1087, Necrophorus Carolina] 

 have provided. 



Accordi-ng to Kirby, 1 a pair or sometimes more than 

 one pair of these insects hunt together. When a dead 

 bird or mouse is found, the pair dig the earth away from 

 under it, thus sinking it ; the female then allows herself 

 to be buried with the carcass until after her eggs are laid, 

 when she finds her way to the surface. The sense of 

 smell is very acute in these beetles, and they exhibit much 

 intelligence. 



The rove beetles or Staphylinidae (No. 1088, Staphy- 

 linus fossator) have become specialized by reduction, the 

 wing covers or elytra being short though still performing 

 the same function, since the large wings can be folded 

 and packed away snugly under them. 



Still more reduced are certain species of Adranes 

 which live in ants' nests. These are blind, with vestigial 

 mouth parts. They are carefully tended by the ants, and 

 in return they secrete a substance which collects on the 

 tips of the elytra and the end of the abdomen. 2 



Among the beetles some of whose larvae are more or 

 less like the Thysanura, those of the Lampyridae are 

 especially interesting, owing to a peculiar modification in 

 their structure whereby light-giving cells are produced. 

 The common fire-fly, Photuris pennsylvanica De Geer, 

 (No. 1089, adult) is luminous in all its stages, though 

 most brilliant in the adult. The light-producing cells are 

 in the abdomen, and they are surrounded by a network 

 of tracheal tubes. The cells contain yellowish white 

 granules which combine with the oxygen brought by the 

 tracheae and thus combustion produces light. This 

 chemical process does not depend wholly upon the life of 

 the insect, since the cells when taken from a dead beetle 

 and crushed in the air are luminous for a time. 3 



1 Text-Book of Ent., 1885, p. 29. 

 2 Can. Ent., XXXIII, Jan., 1901. 



3 See Watase, Woods Hole Marine Biol. Lab., Biol. Lectures, 

 1895. 



