INSECTS EYES. 



5S5 



portion of Brussels lace with hexagonal meyhes 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 

 feasts 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 

 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 ony 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 ofl' 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 vulgana, 

 Cockcliafcr, B, a portion more highly mag- 

 nified, showing the facets of the cornea, and 

 its transparent pyramids, surrounded with 

 pigment. At A they meet, and form the optic 

 nerve. 



