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66 NATURAL HISTORY OF WASPS. 
follow. The ocelli, or simple eyes, have many of the 
same parts as are found in the eyes of some of the 
higher animals, but in a rudimentary condition. The 
cornea or horny membrane, which forms the outer- 
most covering of the organ, is a contimuation of the 
general integument and laminated like it, only made 
transparent. Behind this is a regular lens, with a 
rudimentary iris round its edge. The light enters 
the centre of the lens through the pupil and, travers- 
ing it, is received on a crystalline body which lies 
immediately behind, in contact with the optic nerve. 
The optical arrangements of a perfect eye are to 
be traced here, but in a very rudimentary form. A 
still simpler optical instrument is presented in each 
of the units which go to make up the compound 
eyes. In these the conical crystalline body, which 
is in contact with the optic nerve, is continued direct 
to the cornea, or the horny covering, without the 
intervention of any lens or iris whatever to modify 
the image or control the admission of light. Each 
of these crystalline cones is an eye in itself, separated 
from the adjacent cones by a layer of dark colourmg 
matter. Corresponding to these, the common cornea 
is divided into a number of hexagonal, or sometimes 
quadrangular, facets—many hundreds altogether— 
each a bi-convex lens of a definite curvature differmg 
according to its position. Besides the protection 
which the hardness of the cornea supplies to the 
soft delicate structures beneath, some insects, as the 
honey-bee, have the septa between the facets of the 
cornea armed with hairs—eyelashes as it were— 
placed so as to protect the eyes without obstructing 
vision. | 
