44 0 / Flies. 
have feme of their eyes ready placed towards objcdls 
nearly all round them. 
Two of thefe optick nerves are reprefented as deli¬ 
neated by Mr. Leeuwenhoek, in fig. 84. And in fig, 
85. are exhibited f a great many of them in a duffer, 
as they appeared before the microfcope, whereof that 
part of them which was fituate next the cornea is fhewn 
by the letters NOP; it is alfo obfervable, that thofe 
nerves, which were neareft to the circumference of the 
cornea, were fhorter than thofe next within them, and 
fo on, till they arrive at the central nerve, which is 
the longeft of all. 
The number of the pearls in this fly, Mr. Hook 
r'eckon’d to be 14000. Mr. Leeuwenhoek computed 
6236 in a filk-worm’s two eyes, when in its fly Hate; 
3181 in each eye of a beetle - } and 8000 in the two 
eyes of a common fly. 
Cut off the eye of any fly, and with a pencil, and 
fome clean water, wafh out all the vefiels, thofe veflels 
may be examined by the microfcope, and then if you 
carefully dry the outward covering, fo as not to let it 
fhrink, it will be rightly prepared for making experL 
ments; and upon viewing it, we fliall diftinguifih the 
numerous protuberances or hemifpheres divided from 
one another with a finals light, ifiuing between them, 
and fix tides to each. Mr. Leeuwenhoek having pre¬ 
pared an eye in this manner, placed it a little farther 
from his microfcope than when he would examine an 
object, fo as to leave a right and exad focal diftance 
between it and the lens of his microfcope; and then 
look'd through both, in the manner of a telefcope, at 
the fteepie of a church, which was 299 feet high, and 
750 feet from the place where he flood 5 and could 
plainly 
* Arc. Nat. Ep. 111, 
