422 LUMINOUS INSECTS. 



Beckerheim, Dr. Hulme, and Sir H. Davy, who could 

 perceive no such effect, may perhaps be accounted for 

 by the supposition that in the latter instances the insects 

 having been taken more recently, might be less sensible 

 to the stimulus of the gas than in the former, where pos- 

 sibly their irritability was, as Brown would say, accu- 

 mulated by a longer abstinence : but it is not so easy to 

 reconcile the experiment of Sir H. Davy, who found the 

 light of the glow-worm not to be sensibly diminished 

 in hydrogene gas a , with those of Spallanzani and Dr. 

 Hulme, who found it to be extinguished by the same 

 gas, as well as by carbonic acid, nitrous and sulphuret- 

 ted hydrogene gases b . Possibly some of these contra- 

 dictory results were occasioned by not adverting to the 

 faculty which the living insect possesses of extinguishing 

 its lights at pleasure ; or different philosophers may have 

 experimented on different species of Lampyris. 



The general use of this singular provision is not much 

 more satisfactorily ascertained than its nature. I have 

 before conjectured and in an instance I then related it 

 seemed to be so that it may be a means of defence 

 against their enemies . In different kinds of insects, 

 however, it may probably have a different object. Thus 

 in the lantern-flies (Fulgora), whose light precedes them, 

 it may act the part that their name imports, enabling 

 them to discover their prey, and to steer themselves 

 safely in the night. In the fire-flies (Elater], if we con- 

 sider the infinite numbers that in certain climates and 

 situations present themselves every where in the night, 



* Phil. Trans. 1810, p. 287. b Ibid. 1801, p. 483. 



c See above, p. 225. 



