46 SUPPLEMENT ON 



The larvae of those insects whose metamorphosis is incom- 

 plete, have their eyes the same as in the imago state ; but 

 those whose metamorphosis is complete have only simple 

 eyes, which vary in number in the several species. Cater- 

 pillars, for example, have six on each side, while the larvae of 

 bees, the saw-flies, &c., have only two : many of the last men- 

 tioned kind of larvae, are entirely destitute of eyes. 



The simple eyes of insects are in general too small for 

 dissection, the wonders therefore of their organization are 

 beyond our reach ; these wonders can hardly however be sup- 

 posed to surpass, even should they equal, those which the 

 microscope displays to us in the compound eyes of these 

 curious animals : the structure of these has been fully 

 examined, and is tolerably well understood, though the mode 

 in which the image is formed on the organ is by no means so 

 intelligible to us, as in the case of the larger and vertebrated 

 animals. 



The structure indeed of the compound eyes of insects 

 is so diiFerent from that of the eyes of other animals, even 

 those not far removed in many respects from the moUusca, 

 that we might have had reason to doubt whether these eyes 

 were indeed the organs of sight ; but experiment as well as 

 analogy will determine that they are : thus, if the large hemis- 

 pherical eyes of the dragon-fly be covered with any opaque 

 matter, the insect will strike itself forcibly against the first 

 object in its way ; and if the'compound eyes of the wasp be in 

 like manner rendered impervious to the light, the insect will 

 mount immediately in a vertical direction into the air, re- 

 gardless of any object in its way ; and if the simple eyes of 

 the same wasp be afterwards covered the animal will remain 

 motionless, or at least will not attempt flight. It seems, 

 therefore, by this experiment, in addition to the general ob- 

 servation, that all winged insects have compound eyes either 



