EXTERNAL ANATOMY OF INSECTS. 497 
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 ¢wo ; 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 immoveable, must have them so placed as to enable 
them to do this. This end is accomplished in many 
beetles, for instance Scarabeus L., Heleus, &c., by having 
these organs fixed in the szde 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 (Gyrinus Natator) that I have so often men- 
tioned *, 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. The species of the 
genus Tetraopes, are also so distinguished. In these in- 
sects, one eye’ is above and the other below the base of 
the antennz; in fact, in these the canthus, instead of divi- 
ding the eye partially, as in the other Capricorn beetles, 
runs quite through it at considerable width>. In Rys- 
sonotus nebulosus the eye appears also to be divided in 
two by the canthus. In the Neuroptera Order there is 
more than one instance of the same kind. In Ascalaphus 
there are two considerable eyes on each side of the head, 
which, though clearly distinct, meet like those of many 
@ Vor. IL. p. 4, 367, &c. 
> Prare XXVI. Fic. 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 preusia has also four eves. 
VOL, III. KG 
