ZOOLOGY. 277 



see objects through it. On applying the microscope to the multitude 

 of mirrors, nothing could exceed the singularity of what was seen. " A 

 soldier appeared like an army of pigmies ; for what it multiplied it 

 diminished ; the arch of a bridge exhibited a spectacle more magnifi- 

 cent than any edifice erected by human skill ; and the dame of a candle 

 seemed the illumination of a thousand lamps." The minute regularity 

 of the objects in each of the facets, so disposed as to converge to a cen- 

 tral ganglion, make but a single picture in perception. The great op- 

 tic nerve uniting into a focal point the coincidence of what I)r. Wells 

 designates " the visual direction" impress^ an image intensely concen- 

 trated. The perception of each impression being confined to that of 

 the object immediately in a line with the axis of vision, the impacted 

 lights and shadows of a thousand representations of one and the same 

 form the visual product of a thousand facets give a stereoscopic 

 representation under a thousand adjustments, and render the small 

 organ of the small animal, in power and concentration, a microscope. 



The successive zones in the insect eye modify the rays that pene- 

 trate the sight, passing by each facet, and by the centre of each con- 

 verging cylinder radiating to the optic ganglion. The layer of pig- 

 ment does nothing but diminish the quantity of light, and adjust it. It 

 is found in most if not all diurnal insects, and the iris being perforated 

 with as many holes as there are facets in the cornea, it is subjected to 

 multiplied modifications. As might be expected, this pigment is not 

 met with in any of the nocturnal insects. 



Insects that fly require an ample field of vision. The combined cor- 

 neules become one large pupil. The multiplied facets render super- 

 fluous eyelids and muscles to move the eye. In consequence of the 

 vision being directed to the whole circumference, 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 in- 

 sects which fly by night, like the moths, there is, in place of the black 

 or colored pigment, a substance of a resplendent green, or silvery color, 

 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 phosphores- 

 cent, 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. 



I requested a friend to verify for me Puget's examination of the fa- 

 cetted eye of an insect, by an inspection of the organ under a large 

 microscope. He complied with my request, and sent me the following 

 letter : 



" 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, hav- 

 ' 24 



