498 EXTERNAL ANATOMY OF INSECTS. 



structure with which it has pleased the Creator to di- 

 stinguish the organs of vision of these minute beings, 

 proving, what I have so often asserted, that when ani- 

 mals seem approaching to nonentity, where one would 

 expect them to be most simple, we find them in many 

 cases most complex, I shall now call your attention to the 

 next thing I am to consider — the number of the eyes in 

 question. Most insects have only two s but there are se- 

 veral exceptions to this rule. Those that have occasion 

 to see both above and below the head, the eyes of all 

 being immovable, must have them so placed as to enable 

 them to do this. This end is accomplished in many 

 beetles, for instance Scarabaus L., Helceus Latr., &c, by 

 having these organs fixed in the side of the head, so that 

 part looks upward and part downward ; but in others 

 four are given for this purpose. If you examine the 

 common whirlwig [GyrinusNatator) that I have so often 

 mentioned a , which has occasion, at the same time, to 

 observe objects in the air and in the water, you will find 

 it is gifted with this number of eyes. Lamia Tornator 

 {Cerambyx tetrophthalmus Forst.) and some others, of 

 which I make a genus, under the appellation of Te- 

 trops, are also so distinguished. In these insects, one 

 eye is above and the other below the base of the anten- 

 nae ; in fact, in these the canthus, instead of dividing the 

 eye partially, as in the other Capricorn-beetles, runs quite 

 through it at considerable width b . In Byssonotus Mac- 



a Vol. II. p. 4. 364, &c. 



b Plate XXVI. Fig. 36. h. Fabricius, and after him Olivier, 

 though both quote Forster, regard one of these eyes in Lamia Tor- 

 nator as a spot; but they could not have examined it attentively. 

 Saperda prceusta F. has also four eyes. 



