LESSON 92.] THE EYE IN INSECTS. 295 



the elements are here found of a well-developed visual organ. A 

 distinct optic nerve is given to each simple eye, which at once trans- 

 mits to the brain the image formed upon the retina. 



LESSON XCII. 



THE EYE OF INSECTS, CONCLUDED. 



1335. To show the connection of the optic nerves of the single 

 eyes with the brain, a figure, copied from a preparation of the brain 

 of Mantis religiosa, is given (Fig. 419). The large, well-formed 



FIG. 410. 



Brain, Mantis religiosa. 



cerebrum is shown at a ; posterior to which, at some distance, the 

 cerebellum (5), is seen; the crura, which connect the two hemispheres, 

 are marked c, c ; the optic nerve of the compound eye is shown at d ; 

 the optic lobe is marked e ; the optic filaments, which spring from 

 the optic lobe, are shown at jf ; the nerves distributed to the antennae 

 at h ; the optic nerves of the simple eyes at i, i ; and the bowl- 

 shaped retinal expansion of optic nerves of the simple eyes at k. 



1336. From the mathematical figure of its several component 

 parts, the transparent cornea is an important part of the optical 

 apparatus. Authors have not agreed with regard to its figure ; some 

 claim it to be plano-convex, the plane surface within ; others assert 

 that it is double-convex ; whilst the truth appears to be that it is 

 neither, but, like the human transparent cornea, it is a meniscus 

 (from the Greek, signifying a little moon] ; in other words, it is con- 

 vex on its outer surface, and concave within. 



