ARTHROPODAL VISION. 65 



when this is done by hundreds or thousands of contigiions oinmatidia 

 an image results. All that the painter does who copies an object is to 

 put together patches of light in the same relations of quality and posi- 

 tion that he finds in the object itself, and this is essentially what the 

 compound eye does, so far as can be inferred from its structure." 



Now it appears that Folsoni does not accept Patten's 

 statement that there is a plexus of nerve fibres far up in the 

 crystalline cone, but he believes that such fibres do enter the 

 elongated cells stirrounding the rhabdom and that these cells 

 are themselves the " end organs of vision," 3'et he finds that 

 the light rays are transmitted axially along the rhabdoms to 

 form a mosaic image at the terminii. And having stated that 

 each ommatidium is adapted to transmit light along its axis 

 only, he apparently contradicts the statement as follows: — 



" Rxner, renio\-ing the cones with the corneal cuticula (in L,am- 

 pyris) looked at them from behind with the aid of a microscope and 

 found that the images made bj^ the separate ommatidia were either very 

 close together or else overlapped one another, and that in the latter case 

 the details corresponded ; in other words as many as twentj' or thirty 

 ommatidia may cooperate to form an image of the same portion of the 

 field of vision ; this superposition image being correspondingly l)right 

 — an advantage probably in nocturnal insects." 



If, as claimed by Exner, the whole aggregate ^nelds but a 

 single image, it is evident that the view obtained is of the 

 panoramic order, embracing in some cases an angle of more 

 than 180'^ and including therefore widely separated objects; 

 and of course there is the same comprehensive outlook if a 

 separate, picture is formed in each of the cones, and while it 

 may be difficult for the reader to Ijelieve that the brain of the 

 dragon-fly has the capacity to arrange and utilize twenty-four 

 thousand optical impressions in any given instant, yet it must 

 be remembered that as the angle of a single element, if we 

 include only the cornea and crystalline cone, is probably not 

 less than 20°, many contiguous ommatidia must give practic- 

 ally the same picttire, and further, that the arthropodal nerve 

 system is adapted to the dioptric mechanism, and is far less 



