LUMINOUS INSECTS. 



347 



those species in which, as in the common glow-worm (L. 

 noctiluca), the females are apterous. The torch which the 

 wingless female, doomed to crawl upon the grass, lights up 

 at the approach of night, is a beacon which unerringly guides 

 the vagrant male to her " love-illumined form," however 

 obscure the place of her abode. It has been objected, how- 

 ever, to this explanation, that — since both larva and pupa, 

 as De Geer observed \ and the males shine as well as the 

 females — the meeting of the sexes can scarcely be the 

 object of their luminous provision. But this difficulty 

 appears to me easily surmounted. As the light proceeds 

 from a peculiarly organised substance, which probably must 

 in part be elaborated in the larva and pupa states, there 

 seems nothing inconsistent in the fact of some light being 

 then emitted with the supposition of its being destined solely 

 for use in the perfect state: and the circumstance of the 

 male having the same luminous property, no more proves that 

 the superior brilliancy of the female is not intended for con- 

 ducting him to her, than the existence of nipples and some- 

 times of milk in man proves that the breast of woman is not 

 meant for the support of her offspring. We often see with- 

 out being able to account for the fact, except on Sir E. 

 Home's idea, that the sex of the ovum is undetermined 2 , 

 traces of an organisation in one sex indisputably intended for 

 the sole use of the other. 



I am, &c. 



1 iv. 49. 



2 Phil. Trans. 1799, 157. 



