Of Flies . 47 
br^ne G, G, G, when diverted of its feathers, may 
be feen the orders of pits or holes where the quills are 
jrooted,' and from whence they fhoot; D, E, F, fhews 
a few of the feathers exactly in the form as they 
cover the whole wing. 
Some flies have hairs, and all the fca-rab kind have 
elytra, or cafes, into which their wings are folded and 
preferved, till they want to employ them, as in fig, 
no. fome of thefe cafes reach almoft to the extremity 
of thair tail, as in moft kinds of beetles; and in other# 
are very fhort, as in the earwigg. They do by a very 
curious mechanifm extend and withdraw their mem¬ 
braneous wings. It is very curious to fee them pre*> 
pare themfelves for flight, by thrufting out, and then 
unfolding their wings; and again withdraw thofe joints* 
and neatly fold in the membranes, to be laid up fafe 
in their elytra or cafes; for which fervice the bones 
are admirably placed, and the joints miniftring thereto 
are accurately contrived for the moft compendious and 
commodious folding up of the wings. 
Mr. Hook hath obferved the motion of thefe filmy 
wings in fome minute fpinning flies, which naturally 
jfufpend themfelves as if pois’d and fteady in one place 
of the air, in which by a faint fhadow he could per¬ 
ceive the utmoft extremes of the vibrative motion; 
which fhadow, while they endeavour’d to fufpend them- 
ielves, was not very long; but when they endeavour’d 
to fly forward, it was fomething longer; he alfo fixed 
the legs of a fly with glew or wax upon the top of 
the ftalk of a feather, and then making it endeavour 
to fly away, was thereby able to view it in any pof- 
ture; and found the motion of the extreme limits of 
the vibrations, to be about the length of the body dif- 
tsuxt from each other $ and concluded by the found, that 
