INTERNAL ANATOMY OF INSECTS. 67 
'ptera ; but the vesicles are less numerous, and those at 
the base of the abdomen much larger than the rest a . 
These vesicles, by a very rough dissection, may be di- 
stinctly seen in the abdomen of the cockchafer, which 
appears to be almost filled with them. Not being com- 
posed of cartilaginous rings like the air-tubes, but of 
mere membrane, if a pin pierces one, the air that inflates 
it escapes, and it collapses. In the larva of a little gnat 
(Corethra culiciformis) the trachea appear to proceed 
from a pair of oblong vesicles of considerable size b in 
the trunk, and towards the anus they form two other 
smaller ones c , — upon piercing the former, De Geer ob- 
served a considerable quantity of air to make its escape d . 
Another species, probably of the same genus, described 
by Reaumur, exhibits something similar e . 
But one of the most remarkable structures, in this re- 
spect, is to be seen in the larva and pupa of the dragon- 
flies (Libellulhia). I have before noticed the number of 
their trachecc, 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 larvae abdominal spiracles, is un- 
willing to admit this as a fact f ; 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^. 
* Swamm. Bibl. Nat. t. xvii./ 9. Cuvier Ibid. 440. 
b Plate XXIX. Fig. 10. a. c Ibid. b. 
d De Geer vi. 374. « Rcaum. v. 40. t. vi./. 4, 7. 
f Sprengel Comment. 4. g De Geer ii. 667, 675. 
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