THE FLY. 39 



penetrate into the neighbouring one, and thus cause 

 a confusion of rays ; from each facet, or rather from 

 the apex of each pyramid, a distinct nerve passes into 

 the substance of the eye, and all these nerves meeting 

 in one common centre, form a large nervous trunk, 

 which conveys the image of surrounding objects to 

 the brain. You will therefore see that a perfect image 

 of external objects is admitted into each facet, which, 

 together with its pyramid, partake of the character of 

 a telescopic tube ; and that these images most probably 

 centre in one point, from which the various nervous 

 fibres depart. 



Until recently it was a question much discussed 

 amongst naturalists, whether these remarkable eyes 

 convey to the brain of the Fly, one or many images of 

 the surrounding objects; and the existence of the 

 three simple eyes already referred to, as being placed 

 on the back of the head, by no means tended to the 

 solution of this problem. 



Many were of opinion that each facet of the com- 

 poimd eyes, as also of the simple ones (the former are 

 termed stemmata, the latter oculi), conveyed a distinct 

 image of external objects to the brain, just for instance 

 as we see a series of images on looking through a toy 

 multiplying-glass, which is a prism of many facets. 

 It has, however, of late been shown that such is not 

 necessarily the casej for, although it can be clearly 

 demonstrated that each facet receives a distinct image 

 of surroimding objects, yet, from the position of these 

 facets, which do not all embrace the same view of the 



