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of the Eyes of certain Insects. 
selenitica, the cornea is distributed into facets of only two sizes, 
the transition from the one to the other being very abrupt, the 
consequence of which is, that there is some little irregularity in 
the disposition of the facets at the line of junction, and indeed 
some of them are necessarily not hexagonal, but of an irregular 
figure ; this however, we may infer, does not affect the sight, as 
a circular lens may still be formed in them for the passage of the 
sight, as it is in the regular hexagonal facets, by means of the 
pigment which is distributed in the interstices, and about the cir- 
cumference of all the facets, leaving only circular lenses for the 
transmission of the light. In several dipterous insects however, 
ex. Volucella inanis, there is a gradual transition from the large 
facets which form the upper and generally anterior part of the 
cornea, through facets regularly diminishing in size, down to the 
small ones, of which the lower and posterior part of the cornea is 
composed ; yet, as in the former case of Scceva selenitica, where the 
singular distribution of the facets appears sufficiently accounted 
for by the form and general outline of the eye, so I think in the 
instance just cited, the regular convex form of the eye accounts for 
the gradual diminution of the facets : the more regular the curva- 
ture of the outline of the eye being, the more gradual the transition 
from the large to the small facets, and vice versa. The only in- 
sect possessing a peculiarity in its cornea of this description, which 
I have particularly examined alive, so as to ascertain whether the 
eye in that state presents any peculiar appearance connected with 
the above, is the before-mentioned Libellula, and that presents a 
striking feature in the case ; viz. the part of the cornea occupied 
by the large facets is of a reddish brown colour, and quite opaque, 
whilst the remainder of the eye (comprising the small facets) is of 
that light greenish colour and transparent nature, which every one 
is aw’are the eyes of many insects exhibit when alive. From this 
I infer, that in the case of such insects as the Libellulce, whose 
prominent eyes are particularly exposed to the glare of the sun- 
shine (in which they are most active and on the wing), the opacity 
and large size of the facets in the upper part of the eye modify the 
light admitted in that direction, which otherwise would confuse and 
dazzle the sight of the insect, and by analogy we may reasonably 
presume the same to be the case in the dipterous instances. Another 
observation presents itself — for as the rational presumption is that 
the sight of an insect’s eye is more perfect in proportion to the 
greater number of facets into which it is divided, so the upper part 
of these insects’ eyes must have a less perfect vision than the 
