LUMINOUS INSECTS. 423 



pearing as settled, and sometimes as hovering in the 

 air. — Whatever be the true nature of these meteors, of 

 which so much is said and so little known, it is singu- 

 lar how few modern instances of their having been ob- 

 served are on record. Dr. Darwin declares, that 

 though in the course of a long life he had been out at 

 nights, and in the places where they are said to appear, 

 times without number, he had never seen any thing of 

 the kind : and from the silence of other philosophers of 

 our own times, it should seem that their experience is 

 similar. 



With regard to the immediate source of the lumi- 

 nous properties of these insects, Mr. Macartney, to 

 whom we are indebted for the most recent investiga- 

 tion on the subject, has ascertained that in the common 

 glow-worm, and in Elaier noctilucus and ignittis, the 

 light proceeds from masses of a substance not generally 

 differing, except in its yellow colour, from the intersti- 

 tial substance (corps graisseux) of the rest of tlie body, 

 closely applied underneath those transparent parts of 

 the insects' skin which afford the light. In the glow- 

 ^vorm, besides the last-mentioned substance, which, 

 when the season for giving light is passed, is absorbed, 

 and replaced by the common interstitial substance, he 

 observed on the inner side of the last abdominal seg- 

 ment two minute oval sacs formed of an elastic spirally- 

 wound fibre similar to that of the tracheae, containing 

 a soft yellow substance of a closer texture than that 

 which lines the adjoining region, and affording a more 

 permanent and brilliant light. This light he found to 

 be leas under the control of the insect than that from 



