3 8o 



Microscopical Essays. 



M. De la Hire feems to have been the firfl perfon who dif- 

 covered thefe fmooth eyes. He obferved three of them difpofed 

 in a triangular form, on the back part of the heads of fome of 

 thefe little creatures. He foon found that they were tranf- 

 parent, and thence naturally judged them to be of the fame 

 nature of the cornea of our eyes, and really to ferve the fame 

 office to the creature poflefied of them. 



We find three of thefe fmooth eyes placed triangularly on the 

 back part of the head of vaft numbers of the genera of flies, as 

 well of the two -winged as of the four-winged kinds ; but there 

 are alio fome of both thefe claffes, in which they are wanting, 

 All the fpecies of gnats, and of tipulae, are without them. The 

 heads of thefe are very fmall in proportion to the bulk of their 

 body, and are in a manner covered by their reticular eyes. The 

 want of the fmalr eyes is amply made up by the fize and extent 

 of the larger; but there are fome other kinds which want them, 

 without having this advantage in their place. Of the two-winged 

 flies with fhort bodies, the gad-flies want thefe eyes ; an4 among 

 the longer bodied and four-winged kinds, the flies produced from 

 the puceron-eaters (hemerobius). 



Notwithflanding, therefore, that many fpecies of flies have 

 thefe eyes, there are yet fo many that want them, that Mr. De la 

 Hire would not have judged thefe to be their only eyes, - if he had 

 made experiments on the reticulated ones, in the manner of Mefl'. 

 Swammerdam and Reaumur. Mr. Swammerdam put upon, the 

 eyes of certain flies a covering of black, fteeped in oil ; in this 

 flate they flew at random, and feemed to have- no ftrength ; and 

 wherever they fettled they did not avoid the hand which would 

 Q take 



