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 b f traverses only the cone f, 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 z, after having passed through 

 the cone e. 



"The variously coloured rays given out from the 

 points , 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 situ- 

 ated between a, 6, 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 fila- 

 ments, at first insulated by the pigment, are at 

 length united together into one common and con- 

 tinuous 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 com- 

 mon 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 each 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 distinctness will be reproduced on 

 the sentient surface or retina ; the distinctness 

 of the image of course increasing 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- 



