174 



Microscopical Essays. 



The eyes are generally convex ; they have no eye-brows, the 

 outer tunic is hard and tranfparent, having no external motion, 

 the genus of canceri or crabs excepted. The eyes of the greater 

 number appear, when examined by the microfcope, to be cut 

 into a multitude of little planes or facets, like the facets of a 

 diamond, having to the naked eye the" appearance of net-work. 

 Each of thefe fmall facets is fuppofed to pofleis the powers and 

 properties of an eye. Leeuenhoek counted 3181 of thefe facets 

 in the cornea of a beetle, 8000 in thofe of a fly. As the eyes of 

 in feels are immoveable, they would have loll light of many ob- 

 jects, if their eyes had been framed like thofe of other animals ; 

 but by means of their multiplied eyes, they can eafily view fur- 

 rounding objects : nor is it at all improbable, that, as objects do 

 not appear double to our eyes, but that they are llrengthened, 

 and many falfe appearances are corrected by the ufe of both 5 fo 

 the numerous inlets to fight in an infect may increafe their field 

 of view, augment the intenfity of the light, and be productive of 

 other advantages, of which we can form no conception. The 

 eyes of infects differ in colour, fome being found of every 

 colour, and of inexpremble beauty and brightnefs. 



The antenna are fine and {lender horns, confifling of 

 feveral articulations, moveable jn various directions. They are 

 beautiful in form, of a delicate ftructure, and are placed in the 

 fore part of the head: they vary in different infects, not only in 

 their fhape, their length, their bulk, but alfb in the number of 

 their articulations. The antennae of the male infecl; generally 

 differ from thofe of the female : they form one of the rnofl dif- 

 tinguifhing characterises of infects, and one of the means of 

 judging to what genus they belong. The greatefl number of 

 5 infects 



