248 
DRAGON-FLY. 
out observing that in some species, and parti- 
cularly in the L: varia, grandis, &c. the wonderful 
structure of the cornea or external coat of the eye, 
which prevails in by far the major part of the 
insect tribe, is exhibited with peculiar distinct- 
ness. Even a common magnifier, of about an 
inch focus, demonstrates that the cornea is marked 
by a prodigious number of minute decussating 
lines, giving a kind of chagrin or granular appear- 
ance to the whole convexity : but when micro- 
scopically examined, it exhibits a continued sur- 
face of convex hexagons, and if cut from the head, 
and cleared from its internal pigment, it appears 
perfectly transparent, and seems to consist of an 
infinity of hexagonal lenses of equal convexity on 
both surfaces. This is a subject on which much 
might be said; but the compass of the present 
publication forbids too circumstantial a descrip- 
tion of minute and disputable particulars. It may 
be sufficient to observe that on each eye of this 
animal, according to computation of Leewenhoek, 
there are about twelve thousand five hundred and 
forty-four of these lenses. 
