INTERNAL ANATOMY OF INSECTS. 69 



and appear to serve as reservoirs, since they furnish air 

 by transverse branches to two other tubes ; they have 

 each a recurrent branch, which follows the course of the 

 intestinal canal, and furnishes it with an infinity of bron- 

 chia a . These trachea; are found in the perfect insect. 

 The principal ones in some send forth many branches, 

 terminating in vesicles, which in shape resemble the seed- 

 vessels of some species of Thlaspi, while others appear 

 to form a file of oblong ones h . Near each of their spi- 

 racles also is a vesicle which appears to be a reservoir c . 



But this kind of structure is not confined to insects 

 strictly aquatic. Even such species of terrestrial ones as 

 live upon aquatic plants, and are, consequently, necessa- 

 rily or accidentally often a considerable time under 

 water, are furnished with some apparatus by means of 

 which they can exist in this element for a considerable 

 period. For example, most of the Weevils (Rhyncophora) 

 die in a short time if immersed in water ; yet the species 

 of the genera Tanyspkyrus, Bagous^ and Ceutorliynclms 

 which feed on aquatic plants, can exist for days under 

 water, as I have ascertained by experiment. C. leuco- 

 gaster and another of the same tribe, swims like a Hydro- 

 philus, and will live a long time in a bottle filled with 

 water and corked tight. Other insects also, that are not 

 at all aquatic, have pneumatic pouches. A striated or 

 channeled vesicle I have found under the lateral angles 

 of the collar in the humble-bee, where Chabrier supposes 

 the vocal spiracles are situate ; and also at the mouth of 

 the spiracles of the metathorax in Fespa, &c, d In Sphinx 



a Reaum. vi, 394. Cuv. Anat. Comp. iv. 440. N. Diet. 

 d'Hist. Nat. xvii. 540. 



b PLATE XXIX. FIG. 9. a, b. Reaum, vi. 418-. 450. 

 c Cuv. Anat. Comp. iv. 441. d VOL. III. p. 583, 



