490 M E M O I R S (?/^ the 
^his is the reaf()n, why no infefls will take any food, when they 
are going to change their forms ; and if they do not cleanfe 
thcmfelves as the Libella do, yet they flay a great while longer, 
before they change, without any aliment: The Zihella is not 
lonj^er than half a day in quitting its cale, and taking its flight. 
To know the caufe of its exceeding fwift and whirling motion, 
you muftcut the fkin of the Libe.lla^ which is very fine, all along 
the back, and be fure to carry the point of the Icizzars upwards, 
Icil you cut the interior parts 5 you muft alfo draw the llin to the 
right and left hand, and fix it with pins upon a table, in order to 
difcover the 16 mufcles, which lie between the legs and wings 
(eight on each fide) of the thicknefs, length, colour, and almoft 
the fhape of a orain of barley, contiguous to each other, and 
without any adhefion; you may oblerve, that each mufcle is 
compoled of many flefhy fibres, which do not ieem to be joined 
together, but terminate round at the ends of the mufcle, where 
they compole a common tendon; fo that one might difcern any 
of thefe fibres to be a fmall mufcle, of which the chief mufcle is 
compoled ^ the ufe of thefe mulcks feemed to M. ^oupart very 
particular; for the fame mufcles which ferve to flutter the wings, 
lerve alfo to move the legs; the upper tendons of the mulcles en- 
ter into the wings, the fame, he thinks, as compofe the fibres, 
and the lower enter a good way into the legs ; yet the contrary 
motions of thefe organs are not at all hindered; for as long as 
the wings play, the feet lie ftill, and lerve for a prop to the muf- 
cles, which move the wings ; and when the feet are in motion, 
the wings lie flill, and in their turn lerve to fupport the tendons, 
which direfl the feet : The eyes are like two oblong thick pearls, 
which begin at the fore-part of the head, and end iq the hinder- 
part; their outward membrane is dry, thin, and tranfpai'ent, and 
enclofes a fmall foft ball, filled with a very black liquor ; two 
Imall canals filled with air, enter into each of thefe eyes, and 
run along to the great channel, which is alio furni/hed with air, 
and accompanies the inteftine from the head to the tail ; this 
flru^ture made M. -Poupart \k\\ViV^ that the Libella could derive 
the air, contained in thefe canals into the eyes, to give them a 
greater convexity to view objects that are very near ; and on the 
contrary, the air is forced out of the eyes again, to flatten them, 
v^hen they look at remote objects; and this conjeflure is not alto- 
gether groundleis; for M, yfj/zp^r/ having blown into the thick 
canals, which are about the middle of the hody, the eyes became 
confiderably tumified, and by letting the air return, they became 
Hat again 3 if a Libella is left dead for feme days, the inward 
parts 
