Visual Organs of Insects and Crustacea, 



365 



by the pigment investing the neighbouring cones, will of 

 course produce no effect on any nervous filament placed out 

 of the line m d. The coloured ray d' is therefore perceived 

 only by means of the filament m, on which latter alone it 

 impinges. So also the ray c% given out at the point c, will 

 pass through the whole length of the cone g, and will affect 

 only the corresponding nervous filament /; the ray b' 

 traverses only the cone J", and is perceived only by means of 

 the filament k; and the ray a\ emitted at the point a, is 

 perceived only by means of the filament i, after having passed 

 through the cone e. 



The variously coloured rays given out from the points a, 

 b, c, d, will thus produce in the interior of the eye a deter- 

 minate figure, corresponding to the luminous object without ; 

 and the same remarks will necessarily apply to any number 

 of points situated between a, b, c, d. 



Each nervous filament conveys to the bulb of the optic 

 nerve the impression of the ray which it has individually 

 received ; and, as all the nervous filaments, at first insulated 

 by the pigment, are at length united together into one com- 

 mon and continuous bulb or nervous expansion, the im- 

 pression received by each filament is united to those of all 

 the others in the bulb of the optic nerve, and so a common 



