INTERNAL ANATOMY OF INSECTS. 67 
a pair of oblong vesicles of considerable size? in the trunk, 
and towards the anus they form two other smaller ones?, 
—upon piercing the former, De Geer observed a consi- 
derable quantity of air to make its escape®. Another spe- 
cies, probably of the same genus, described by Reaumur, 
exhibits something similar‘4. 
But one of the most remarkable structures, in this re- 
spect, is to be seen in the larva and pupa of the dragon- 
flies (Libellulina). I have before noticed the number of 
their trachee, but I shall here describe their whole in- 
ternal respiratory apparatus. I must observe that Reau- 
mur, Cuvier, and most modern writers on the physiolo- 
gical department of Entomology, have affirmed that they 
respire the water, and that they receive it for that pur- 
pose at their anal extremity: but M. Sprengel, from 
having observed in the larvee abdominal spiracles, is un- 
unwilling to admit this as a fact*; and De Geer also 
seems to hesitate upon it, especially as he discovered that 
the animal seemed to absorb the water to aid it in its 
motions‘. But when we consider that it is by the action 
of a pneumatic apparatus that the absorption and ex- 
pulsion of the water takes place, and that the animal 
when it has been taken out of that element, upon being 
restored to it, immediately has eager recourse to this ac- 
tion’, we shall feel inclined rather to adopt the opinion 
of those great physiologists Reaumur, Lyonnet, and 
Cuvier, and admit that it absorbs water for the purpose 
of respiration. 1 shall now explain how this takes place. 
4 Prare XXIX. Fre. 10. a. b Tbid. 3. 
© De Geer vi. 374. 2 Reaum. v. 40. é. vi. f. 4, 7. 
© Sprengel Comment. 4. £ De Geer ii. 667, 675. 
* Reaum. vi. 394—. 
