INSECTS. 291 



compared with the space they occupy) of minute, regular, geometrical 

 hexagons, well defined, and capable of being computed with tolerable 

 ease, their exceeding minuteness being taken into consideration. 

 When viewed in this way, the entire surface bears a resemblance to 

 that which might easily and artificially be produced by straining a por- 

 tion of Brussels lace with hexagonal meshes over a small hemisphere of 

 ground glass. That this gives a tolerably fair idea of the intricate 

 carving on the exterior, may be further shown from the fact, that deli- 

 cate and beautiful casts in collodion may be procured from the surface, 

 by giving this three or four coats with a camel-hair pencil. When dry, 

 it is peeled off in thin flakes, upon which the impressions are left so 

 distinct, that their hexagonal form can be discovered with a Coddington 

 lens. This experiment will be found useful in examining the configu- 

 ration of the facets of the hard and unyielding eyes of many of the Co- 

 leoptera, in which the reticulations become either distorted by corruga- 

 tion, or broken by the pressure required to flatten them. It will be 

 observed also, that by this method perfect casts can be obtained without 

 any dissection whatever ; and that these artificial exuviae for such they 

 really are become available for microscopic investigations, obviating 

 the necessity for a more lengthened or laborious preparation. The dis- 

 section 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 portion of the hairs cut 

 off at the end, which is thereby flattened. 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 j and the coloured pig- 

 ment on the interior may be scrubbed off by this simple process, A 

 brush thus prepared, and slightly moistened, forms, as far as my expe- 

 rience goes, by far the best forceps for manipulating these objects pre- 

 paratory to mounting ; as, if only touched with any hard-pointed sub- 

 stance, they will often spring from the table from mere elasticity, and 

 thus the labour of hours be lost in a moment. It does not appear to 

 me desirable to attempt to flatten an entire cornea by pressure and 

 maceration, although this is generally recommended, as -ifc does not 

 either aid in developing the beauty, or counting the number of its 

 lenses. On the contrary, the rounded membrane becomes, if the mar- 

 gin remains intact, corrugated ; and so one hexagon overlaps the other. 

 It will be useful, therefore, to make two preparations of the eyes of one 

 insect : the one entire, retaining its natural curved form, not having 

 been subjected to pressure ; the other nicked at its margin, or cut into 

 small fragments, and pressed between two slides. 



