EXTERNAL ANATOMY OF INSECTS. 623 
those tribes of the former Order, whose wings are with- 
out nervures, the areas are often marked by folds. 
M. Chabrier has observed that in Coleoptera the spe- 
cific weight of the margin of the wing, and its means of 
resistance, are augmented by a liquid which is introduced 
at the will of the animal, into a long pocket under the 
brachial, here called the costal and mediastinal nervures, 
covered by a supple membrane, which in a state of repose 
becomes flaccid *: it is easily detected, being of a paler 
colour than the nervures between which it lies; this is 
what I call the Phialum; we have before seen that it 
exists also in Elytra and some Hemelytra® ; but I have 
not detected it in any other wings. 
I have before given you a sufficiently full account of 
the alule or winglets of Diptera* ; and shall here only 
observe that they are not confined to one particular tribe, 
as has been usually imagined; but though sometimes 
extremely minute, simple, and not easily detected, are an 
universal distinction of the Order. 
Having thus endeavoured to elucidate the /arger Areas 
into which wings appear to be divided; I shall next say 
something on the smaller ones produced by the intersec- 
tion or ramification of the nervures; these had been 
named areolets (areole) several years before M. Jurine’s 
work, in which he calls them, I think zmproperly, cellules 
(cellule), was published; I therefore retain the prior 
term. The general structure of the nervures of the wings 
of insects having been before explained 4, I shall not 
here repeat what I then said ; but there is a curious cir- 
cumstance. connected with it, particularly visible in the 
1 Sur le Vol des Ins. c. i. 428. » See above, p. 598, 614. 
© Vou. I. p. 354—. See above, p. 557. * Von, II. p. 342—. 
