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 (Libellufina). I have before noticed the number of 

 their trachea, 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. JBibl. Nat. t. xvii./. 9. Cuvier Ibid. 440. 



b PLATE XXIX. FIG. 10. a. c Ibid. b. 



d De Geer vi. 374. * Reaum. v. 40. t. vi./. 4, 7. 



f Sprengel Comment. 4. E De Geer ii. 667, 675. 

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