Microscopical Essays. 



brane is another, which is more delicate and more tranfparent;, 

 but connected with it by means of pulmonary tubes ; under this 

 there is placed a fecond fpecies of fibres, tranfverfely applied, like 

 fo many beams, to fupport the pyramidal fibres that are laid 

 over them. 



Each fide of the head of a fly, which is cut as it were into a 

 multitude of fmall facets, is one of the reticulated eyes of the 

 creature. Nature allots two of thefe reticulated eyes to each fly ; 

 and as they each contain fuch a vaft multitude of fmaller, but 

 perfecl eyes, one would imagine them to be very fuffieient for all 

 the occafions of the animal. There are, however, certain flies of 

 the ephemera kind which have four of thefe reticulated eyes, two 

 of which are placed as is ufual in the mufca, and are but of fmall 

 extent ; the other two have each the appearance of a fort of tur- 

 ban, and are placed one befide the other upon the upper part of 

 the head. 



Thefe have fomewhat the figure of a mufhroom, the head of 

 it extended a little beyond the ftalk, and the upper convex fur- 

 face cut into almoft an innumerable quantity of facets. 



The firft pair of the reticular eyes of this fly, which are placed 

 as thofe of the other flies, are in colour brown ; thofe of the 

 mufhroom form are of a very beautiful citron- colour, and as 

 tranfparent as the moft pellucid reticular eyes of other flies ; for, 

 among the various fpecies, fome have thefe eyes much more 

 tranfparent than others. The fly, thus remarkably furni fried 

 with eyes, is produced from a worm of the fame kind with the 

 common fpecies of ephemerons ; it's body is of a pale yellow,. 



andi 



