70 INTERNAL ANATOMY OF INSECTS. 
Ligustri the bronchia terminate in oblong vesiculoso- 
cellular bodies, almost like lungs 3 ; in Smerinthns Tilice 
these are preceded by a simple vesicle bound with spiral 
fibres b . M. Chabrier thinks that these air-bladders of 
insects, amongst other functions, give more fixity and 
force to the muscles for flight c . 
Many physiologists have seen an analogy between the 
spiral vessels of plants and the trachea? of insects ; and 
some of great name, as Comparetti, Decandolle, and 
Kieser, have thought that in some instances they termi- 
nated in the oscula or cortical pores : but Sprengel con- 
tends that they are not accurate in this opinion d . In 
fact, the principal analogy seems to be in the spiral 
structure of both these vessels. 
Having considered the different organs of respiration 
both external and internal, I shall make a few further 
observations upon this function. We know little more 
respecting the mode in which insects respire, except that 
they breathe out the air by the same kind of organs by 
which they receive it, — namely, the spiracles, or their re- 
presentatives. This has been satisfactorily proved by 
Bonnet, who showed that the experiments by which 
Reaumur thought it established that insects inspire by 
their spiracles, but expire through the mouth, anus, or 
pores of the skin, are founded on an erroneous assump- 
a Sprengel Comment. 17. t. m.f. 24. 
» Ibid.t. If. 11. 
c Sur le Vol des Ins. c. ii. 336. note 1. 
d Sprengel Comment. 13 — . These oscula or pores in the straw 
of Triticum hybernum, as figured by Mr. Bauer's admirable pencil, 
(Sir J. Banks On the Blight, $c. f. ii./. 3.) exactly resemble the spi- 
racles of insects. 
