70 INTERNAL ANATOMY OF INSECTS. 



Ligustri the bronchice terminate in oblong vesiculoso- 

 cellular bodies, almost like lungs a ; in Smerinthus 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. iii./. 24. 



* Ibid.t.i.f.ll. 



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 Slight, $c. t. ii./. 3.) exactly resemble the spi- 

 racles of insects. 



