106 Insect Vision and Insect Sleep. 



doubt, we must prove our premises, that is, if the facettes of an in- 

 sect's eye, composed originally of an immense number of spheres of 

 equal size, equally pressed, laterally, pass into the hexagonal form, or 

 suffer any other modification. 



" That they are of equal size is manifest from simple inspection. 



" We will now see if experiments prove they are, or have been, 

 spheres ; but I must first speak of some further examination of the 

 cornea. 



" I counted the number of facettes, or faces, by the micrometer, 

 and found in each eye 12,500, but I think they are somewhat more 

 numerous. 



" Around each facette I found a fringe of fine hairs, which seem 

 to fulfil the purpose of eyelashes. 



" I now placed the cornea in such a manner, that, in looking 

 through the microscope, and through the cornea, I could see the 

 flame of a candle. I then saw, not one flame, but an immense 

 number of flames ; in fact, an illumination of candles on a large scale, 

 which arrangement quite corresponded with the hexagonal form of 

 the facettes : thus there was a row of flames, and above this another 

 row, not one flame above another, but intermediate flames in inter- 

 mediate rows, and so on one row with another. 



" Each facette is then a distinct eye, producing a distinct image 

 in each facette. 



" An ordinary observer might infer that the insect saw not one 

 object, but a multitude of objects ; not one flower, but thousands, 

 producing a complete ' embarras de richesses,' most confusing to 

 the poor fly. It is natural that we should be led to such a conclu- 

 sion. But, on the other hand, we are taught by analogy that ' order 

 is Nature's first law.' To help us to the clue of this second point, 

 or of this apparent confusion, we will continue our experiments. 



" Taking for granted that spheres were upon the disk, I severed 

 them with a needle and found one end of the several pieces circular, 

 and the other pointed ; in fact, each separate ocellus, or eye, had the 

 form of a cone, the basis forming the facette, and the apex converg- 

 ing to a centre. Each was embedded in a mass of pigment — in plain 

 terms, black paint ; with each apex receiving a filament of the optic 

 nerve. Each separate ocellus, therefore, has a separate power of 

 vision. 



" Each facette, cone, and filament being separated from all other 

 facettes, cones, and filaments by a layer of pigment, forms a separate 

 ocellus, so circumstanced that no ray of light received by one passes 

 into another, and all the filaments being severed from each other by 

 the pigment, they in no way interfere with one another. 



" We now see, by experiment, that as each ocellus takes up a 

 distinct picture, each picture is, necessarily, slightly altered in per- 

 spective. The images, by the direction of the facetted mirrors 

 severally, are each slightly varied ; but being united on the central 

 ganglion, they form one perception of one object, or one scene. This 

 is only a multiplication of the incidents of our own vision with two 

 eyes. If we close one eye, we sec an object in a certain perspective ; 

 if we close that eye that was open, and open that which was shut, 



