66 INTERNAL ANATOMY OF INSECTS. 
is a singular anomaly, as the other Gistride have only 
a pair of trachee?*. 
ili. Respiratory Sacs or Pouches. Besides their trachea 
and bronchi, many insects are farnished with a kind of 
reservoir for the air, under the form of sacs, pouches, or 
vesicles. These are commonly formed by the bronchial 
tubes being dilated at intervals, especially in the abdo- 
men, into oblong inflated vesicles; from which other 
bronchial tubes diverge, and again at intervals expand 
into smaller vesicles, so as to exhibit no unapt resem- 
blance—as Swammerdam has observed with respect to 
those of the rhinoceros-beetle—to a specimen of Fucus 
vesiculosus. Cuvier compares them in the Lamellicorn 
beetles in general to a tree very thickly laden with leaves”; 
and Chabrier observes that they particularly occur in the 
intestinal canal®. This structure of the pulmonary or- 
gans may be seen also in the common hive-bee, and other 
Hymenoptera ; but the vesicles are less numerous, and 
those at the base of the abdomen much larger than the 
rest’. These vesicles, bya very rough dissection, may 
be distinctly 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 trachee appear to proceed from 
a Essay on the Bots, &c. 49. Valisnieri 1. 101. ¢. vi. fi 4. &c. 
b Bibl. Nat. i. 149. a. t. xxix. fia. Cuv. Anat. Comp. iv. 439. 
Malpigh. De Bombyc. t. 11. f. 2. 
© Sur le Vol des Ins. c. ii. 336. note 1. 
4 Swamm. Bibl. Nat, t. xvii. f. 9. Cuvier Ibid. 440. 
