1446 THE STORY OF THE UNIVERSE 



bodies represents a perfect eye; every one is fur- 

 nished with all the apparatus and combinations req- 

 uisite for distinct vision; and there is no doubt that 

 the dragon-fly looks through them all. In order to 

 explain this, I must enter into a little technical ex- 

 planation of the anatomy of the organs, as they have 

 been demonstrated by careful dissection. 



The glassy convex plate or facet in front of each 

 hexagon is a cornea, or corneule, as it has been called. 

 Behind each cornea, instead of a crystalline lens, 

 there descends a slender transparent pyramid, whose 

 base is the cornea, and whose apex points toward the 

 interior, where it is received and embraced by a 

 translucent cup, answering to the vitreous humor. 

 This, in its turn, is surrounded by another cup, 

 formed by the expansion of a nervous filament aris- 

 ing from the ganglion on the extremity of the optic 

 nerve, a short distance from the brain. Each lens- 

 like pyramid, with its vitreous cup and nervous fila- 

 ment, is completely surrounded and isolated by a 

 coat (the choroid) of dark pigment, except that there 

 is a minute orifice or pupil behind the cornea, where 

 the rays of light enter the pyramid, and one at the 

 apex of the latter, where they reach the fibres of the 

 optic nerve. 



Each * cornea is a lens with a perfect magnifying 

 power. The focus of each cornea has been ascer- 

 tained by similar experiments to be exactly equal to 

 the length of the pyramid behind it, so that the image 

 produced by the rays of light proceeding from 

 any external object, and refracted by the convex 

 cornea, will fall accurately upon the sensitive termi- 



