COMPARATIVE PHYSIOLOGY OF VISION. 



177 



Fig. 107 



the figure. They are of a horny 

 texture, and perfectly transpa- 

 rent. Each corneule has the 

 form of a truncated pyramid, 

 the length of which is between 

 two and three times the diame- 

 ter of the base. 



543. These little eyeglasses, 

 as shown by the figure, stand 

 around the nervous bulb g, 

 which may be considered the 

 retina, or optic ganglion, and 



on which is painted the images of objects, as they are on 

 the retina of animals ; each corneule being of itself a per- 

 fect eye, and, according to Duges, furnished with a pupil, 

 which he saw contracting and dilating in proportion to 

 the quantity of light. 



544. Fig. 108 represents some of these tubes, more 

 highly magnified, in order to show their precise forms. The 



' Fig. 108. 

 ,05 



letters u, v, x, in this and the last figure correspond. The 

 dark part is a black pigment which fills a portion of the 

 diameter of each tube, the aperture widening at v, where 

 it is filled with a vitreous humor. 



545. It thus appears that each eye forming these vast 

 aggregates, consists of a distinct tube, furnished with all 

 the anatomical parts necessary for perfect vision ; and thus 

 has nature supplied the want of motion in this organ, by 

 a multiplication of their numbers, so that the insect has a 

 distinct eye, pointed toward the object, in whatever direc- 

 tion it may appear. 



546. That there might be no doubt that insects have 

 as many eyes as there are tubes in each, Leeuwenhoek, 

 having prepared the compound cornea of a fly for the 

 purpose, placed it a little more remote from his micro- 



