Insect Vision and Insect Sleep. 105 



render superfluous eyelids and muscles to move the eye. In 

 consequence of the vision being* directed to the whole circum- 

 ference, it comprehends, by relative adjustment, all objects 

 around. A simpler eye occurs in the grovelling insects that 

 see only what is near with distinctness. In insects which fly 

 by night, like the moths, there is, in place of the black or 

 coloured pigment, a substance of a resplendent green, or silvery 

 colour, serving not to absorb, but to reflect the rays of light, 

 and enabling them to see by a more obscure illumination than 

 that of daylight. The eyes of moths look always luminous, and 

 appear as if they were phosphorescent, from this reflecting 

 power. This organization gives a solution to the reason why 

 moths fly to the candle. They lose all discernment in the blaze 

 of radiance that overwhelms them by reflection; and they perish 

 in the flame into which they rush. 



After I had entered among my notes the preceding memo- 

 randum, I requested my friend, Mr. Toase, to verify for me 

 Puget's examination of the facetted eye of an insect, by an in- 

 spection of the organ under his excellent large microscope. He 

 kindly complied with my request, and sent me the following 

 interesting letter : — 



" Kingston, 21sfc January, 1861. 



"My dear Sir, — I have taken a dragon-fly (Libellula) as the 

 study of the eye of an insect. * * * 



" The eye was first simply removed from the head of the dragon- 

 fly and examined under a good lens : — seen thus, it seemed as if it 

 were covered with intensely small drops of water, something like 

 dew. 



'• The eye was next immersed in solvents, and cleaned with a 

 fine camel' s-hair brush, leaving nothing behind but the cornea. This 

 to the naked eye had the appearance of a white transparent horny 

 substance, having the form of a shallow cup. 



■ " It was now placed under a microscope with a power of 250 

 diameters, or magnifying 62,500 times. 



" Under this power the bead-like appearance, noticed with the 

 simple lens, resolved itself into a definite form, resembling precisely 

 the cells of the honeycomb as they appear on the broad plane. 

 Like these cells, each division was hexagonal. The substance of 

 each division was convex exteriorly. We are reminded that this is 

 the form which economizes space the most, and that it is also the 

 form always taken by the equal sized round bodies when equally 

 pressed together. This law we see exemplified in the cellular tissue 

 of plants, and we account for the elongated form of the cells of the 

 fibrous tissue, by unequal pressure. We see this law in the formation 

 of the cells of the honeycomb, as equally sized globular cells equally 

 pressed laterally and forming hexagonal cells. We see it again, 

 though imperfectly, it is true, in soap bubbles. Might we not, there- 

 fore, infer that this peculiar form is the natural effect of a known law, 

 and that it could not assume any other form ? But to remove all 



