140 INSECT MISCELLANIES. 



c, will pass through the whole length of the cone g, 

 and will affect only the corresponding nervous fila- 

 ment I ; the ray h' traverses only the cone /, 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 determinate figure, corresponding to the 

 luminous object without ; and the same remarks will 

 necessarily apply to any number of points situated be- 

 tween a, b, Cj 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 fila- 

 ments, at first insulated by the pigment, are at length 

 united together into one common and continuous bulb 

 or nervous expansion, the impression received by each 

 filament is united to those of all the others in the bulb 

 of the optic nerve, and so a common and continuous 

 image is produced. Rays coming from one point of a 

 remote object will, it is true, illuminate throughout 

 more than a single cone ; and then, to eacli luminous 

 point without, there will correspond in the interior of 

 the eye, not exactly a single illuminated point, but 

 rather a little circle of diffused or dispersed light ; 

 and, in consequence, an image of but little distinct- 

 ness will be reproduced on the sentient surface or 

 retina 5 the distinctness of the image of course in- 

 creasing in proportion as the object approaches the 

 eye. 



' The image in the interior of the eye will be more 

 distinct, precisely as the cones, in a given portion of 

 the eye, are more numerous ; the distinctness will 

 also increase in proportion to the length of the 

 cones ; for the longer the cones are, the more com- 

 pletely will all rays entering them obliquely be pre- 



