INSECTS EYES. 



585 



portion of Brussels lace with hexagonal meshes over a 

 small hemisphere of ground glass. That this gives a toler- 

 ably fair idea of the intricate carving on the exterior may- 

 be further shown from the fact, that delicate and beautiful 

 casts in collodion can be procured from the surface, by 

 giving it three or four coats with a camel-hair pencil. 

 When dry it peels off in thin flakes, upon which the 

 impressions are left so distinct, that their hexagonal form 

 can be discovered with a Coddington lens. This experi- 

 ment will be found useful in examining the configuration 



o o 



of the facets of the hard and unyielding eyes of many of 

 the Coleoptera, in which the reticulations become either 

 distorted by corrugation, or broken by the pressure re- 

 quired to flatten them. It will be observed also, that by 

 this method perfect casts can be obtained without any dis- 

 section whatever ; and 

 that these artificial 

 exuvice — for such they 

 really are — become 

 available for micro- 

 scopic investigations, 

 obviating the necessity 

 for a more lengthened 

 or laborious prepara- 

 tion. The dissection 

 of the cornea of an 

 insect's eye is by no 

 means easy. I have 

 used generally a small 

 pair of scissors, with 

 well - adjusted and 

 pointed extremities, and a camel-hair pencil, having a por- 

 tion of the hairs cut off at the end, which is thereby flat- 

 tened. The extremity of the cedar handle should be cut 

 to a fine point, so that the brush may be the more easily 

 revolved between the finger and thumb ; and the coloured 

 pigment on the interior may be scrubbed off by this 

 simple process. A brush thus prepared, and slightly 

 moistened, forms by far the best forceps for manipulating 

 these objects preparatory to mounting ; as, if only touched 

 with any hard-pointed substance, they will often spring 

 from the table and be lost. 



Fig. 262. 



A, is a section of the eye of Melolontha rmlgana, 

 Cockchafer. B, a portion more highly mag- 

 nified, showing the facets of the cornea, and 

 its transparent p)raraids, surrounded with 

 pigment. At A they meet, and form the optic 

 nerve. 



