INSECTS. 1 1 



in some insects, as in Spiders, they are six 

 or eight in number. In the major part of 

 the Insect tribe thi may be considered as 



compound; at least with respect to the exterior 

 coat or cornea, which, when viewed with a mi- 

 en >cope, presents the appearance of an infinite 

 number of separate convexities, which are of a 

 shape exactly hexagonal, and appear to be so 

 many real convex lenses or glasses; but the exact 

 manner in which vision is performed in Insects is 

 perhaps not yet ascertained. Some have supposed 

 each of the hexagonal lenses to act as a real and 

 separate eve, and that the optic nerves are ex- 

 panded in separate branches at the bottom of 

 each as a retina; or that one universal retina is 

 expanded under all, which probably, is the real 

 structure. Yet it still remains difficult to account 

 for this~prodigious multitude of eyes on the head 

 of one single animal. The head of the common 

 Libellula or Dragon-Fly is perhaps furnished with 

 not less than twenty-five thousand of these little 

 lenses. AVhatever be their use, this particular 

 structure cannot be contemplated without the 

 highest admiration, and constitutes one of the 

 most curious particulars in the comparati\e ana- 

 tomy of Insects. That they are real convex lenses 

 seems demonstrated by their exhibiting every 

 phenomenon of such; inverting any object viewed 

 through them when magnified, as the flame of a 

 candle, the chimney of a house, or any other 

 object towards which they are directed; and that 

 they are double-convex lenses has been generally 



