COMPARATIVE PHYSIOLOGY OP VISION. 



181 



Fig. 107. the figure. They are of a 



horny texture and perfectly 

 transparent. Each corneule 

 has the form of a truncated 

 pyramid, the length of which, 

 is between two and three times 

 the diameter of the base. 



These little eye glasses 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 

 perfect eye, and according to Duges furnished with a 

 pupil, which he saw contracting and dilating in propor- 

 tion to the quantity of light. 



Fig. 108 represents some of these tubes more highly 

 magnified, in order to show their precise forms. The 



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

 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. 



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 towards the object, in 

 whatever direction it may appear. 



That there might be no doubt, that Insects have 33 



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- 



16 



