490 PHYSIOLOGY. 



the metamorphosis, it appears to take place especially during the 

 pupa state, and, indeed, by the compound eyes being gradually 

 developed from the simple ones. Pupae, however, have the entire 

 cornea immediately after stripping oft' their larva-skin ; and in the pupa 

 of Siratiomys Joh. Muller found beneath it the glass lens and the 

 layer of pigment yet but slightly coloured. If now this composition of 

 compound eyes from simple ones actually takes place, which cannot 

 very well be doubted, it may serve as a guide to the explanation of the 

 parts of the compound eye, which I would thus explain : the glass lens 

 corresponds with the glassy body, the lens with the thick cornea, and 

 this latter with a superficial thin layer of the entire cornea, which it 

 likewise is, and which is peeled off during the metamorphosis. After 

 the last moult this layer grows to the lens, and they then both appear 

 as identical, but, in relation to the other parts, merely as a thick layer 

 of the cornea. Hence the compound eyes of insects consist of the same 

 parts as the simple eyes. 



SEVENTH CHAPTER. 



THE LUMINOUSNESS OF INSECTS. 



279. 



THE peculiar light which many insects, but chiefly beetles, display, 

 is a very remarkable phenomenon. We have deferred its consideration 

 to the end of somatic physiology, as it does not appear to stand in direct 

 connexion with either of the four chief functions of the animal body, 

 but may be considered rather as the result of an entirely peculiar vital 

 phenomenon, the cause of which has been by no means thoroughly 

 ascertained. We will defer communicating the results of the experi- 

 ments made upon this highly interesting subject to the end of this 



V 



chapter, and first mention those insects in which this peculiar luminous- 

 ness has been observed. 



The majority of them belong to the Colcoptera, and indeed to two 

 families which also in .other respects present a tolerable affinity . These 



