THE HONEY-BEE. 



terminates against an expansion of the optic nerve. 

 The eminent physiologist, Dr. W. B. Carpenter, says, 

 in describing the minute structure of these organs : 

 " The interior of this pyramid is occupied by a trans- 

 parent substance, which represents the vitreous 

 humour (of the eyes of vertebrates), and the pyramids 

 are separated from each other by a layer of dark 

 pigment, which completely incloses them, save at 

 the pupillary apertures, and also at a corresponding 

 set of apertures at their smaller ends, where the 

 pigment is perforated by the fibres of the optic nerve, 

 of which one proceeds to each separate eye. Each 

 facet, or 'corneule' of the common cornea, is convex 



Fig. 26,— Facets of Eye of a Bee. 



on both its surfaces, and thus acts as a lens, the focus 

 of which has been ascertained, by experiment, to be 

 equivalent to the length of the transparent pyramid 

 behind it ; so that the image produced by the lens 

 will fall upon the extremity of the filament of the 

 optic nerve, which passes to its truncated end. The 

 rays which have passed through the several 'cor- 

 neules'are prevented from mixing with each other 

 by means of the layer of black pigment which sur- 

 rounds each cone ; and thus, no rays, except those 

 ■which correspond with the axis of the cone, can reach 

 the fibres of the optic nerve. Hence it is evident 

 that each separate eye must have an extremely 



