and smooth or simple Eyes of Insects. 2/5 



<Jonvmced by squeezing them, or rather by rubbing off from 

 them a black stratum which might intercept the action of the 

 xays of light. The insects subjected to this test act completely 

 as if blind, and can no longer direct their efforts rightly for any 

 of the purposes of their existence. These experiments have 

 Ijeen so often repeated, and are so easily performed, that there 

 is now no naturalist who doubts that the parts called eyes^ in 

 insects, really serve all the puqjoses of vision. But how can 

 these eyes concur to vision, and give the insect the faculty of 

 distinguishing objects clearly? These organs, we have said, are 

 constructed in sucli a way as to fit them to receive the images 

 from objects, by the simple shock of the ravs which these ob- 

 jects reflect ; and from this way of feeling there must result an 

 extremely lively imprpssion. Insects not having, like vertebral 

 animals, a contractible pupil, it seems that, as a consequence of 

 this organization, vision ought to be very perfect among them, 

 on account of the great number of rays which fall continually 

 oil the facets of their eyes. Thus these animals seem to distin- 

 guish objects at very considerable distances; but the images are 

 painted or stop on their choroid, or they pass beyond, which is 

 very difficult to ascertain, although the first opinion seems most 

 probable. 



One of the most learned naturalists of Geneva, M. Prevost, 

 bars recently hazarded an opinion \ery different from that which 

 Ave here propose, for he thinks that insects are completely rwyopes. 

 He remarks in the first place, that if wc prepare two lenses of 

 the same form and substance, their local distances will be in 

 proportion to their diameters, and in general that all the images 

 of points similarly situated will be also similarly situated. This 

 principle being granted, and true in itself, M. Prevost applies it 

 to insects ; but in our opinion the consequences he draws from it 

 iu-e not well founded. " If the eyes of insects," he observes, 

 *^ were of the same materials as ours are, and of forms precisely 

 similar, these animals would be singularly myopes; for, in order 

 that the image of any object may be painted exactly on their 

 retina, the distance from the object to the eye would also re- 

 quire to be equally small with respect to the distance required 

 for the hiiman eye, as is the diameter of their eye with respect 

 to the diameter of ours." That this reasoning may be applica- 

 ble to insects, there must be a perfect similitude between the 

 matter and the forri! of their eyes and ours ; but we know that 

 there is not the slightest relation between these organs. In 

 fact, the description which we have given of the two species of 

 the eyes of insects, proves that these eyes do not present, as ad- 

 mitted by M. Prevost, different transparent humours, nor liga- 

 S 2 meiit« 



