INTERNAL ANATOMY OF INSECTS. 59 
lamin or false gills filled with air-vessels ; but instead 
of being ventral, they proceed from the anus. ‘They are 
three in number, one dorsal and two lateral, perpendi- 
cular to the horizon, of a lanceolate shape, beautifully 
veined, with a longitudinal middle nervure, from which 
others diverge towards the margin, which are probably 
bronchie. ‘They are used by the animal, which swims 
like a fish, as fins, but it does not appear to imbibe the 
water like the other Libelluline, nor to propel itself by 
ejecting it,—a circumstance which furnishes an additional 
argument for the more received opinion, that this action 
in them is for the purpose of respiration as much as 
for motion ?. 
The larvee and pup of the Libelluline, receive the 
water and air that they respire by a large anal aperture, 
which is closed at the will of the animal by five hard, 
moveable, triangular, concavo-convex pieces, all very 
acute and fringed with hairs. These pieces are placed 
so that there is one above, which is the largest of all; 
one on each side, which are the smallest, and two below ; 
when these are closed, they form together a conical point”. 
Sometimes only three of these pieces are conspicuous : 
three other cartilaginous pieces, resembling the valve 
of a bivalve shell, close the passage within the pointed 
pieces’. At this orifice the water is received; and when, 
by an internal process to be described afterwards, it has 
parted with its oxygen, is again expelled. 
Under this head I shall mention a fact which may be 
connected with respiration of the insects concerned. In 
@ Vor. IIL. p. 154. De Geer ii. 697—. t. xxi. f. 4, 5, 12. 
> De Geer Ibid. 666—. t. xix. f. 6. 
© Reaum. vi. 393. t. xxxvi. f. 8, 9. ¢, t. 
d-Jbid. 395. t. xxxvi. f. 8-—9. c. c. 
