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 b . 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 (Ithyncophora) 
die in a short time if immersed in water ; yet the species 
of the genera Tanysphyrus, Bagous, and Ceutorhynchus 
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 Vespa, &c. d In Sphinx 
3 Reaum. vi. 394—. Cuv. Anal. Comp. iv. 440—. N. Diet. 
d'Hist. Nat. xvii. 540—. 
b Plate XXIX. Fig. 9. a, b. Reaum. vi. 418-. 450. 
' Cuv. Anal. Comp. iv. 441. ' Vol, III. \\ 583. 
