72 INTERNAL ANATOMY OF INSECTS. 



insect's in general, are destined for the escape of the air, 

 after it has parted with its oxygen, received by the anal 

 ones a . So that there seems very good ground for 

 M. Chabrier's opinion that inspiration is ordinarily by 

 the abdominal spiracles, and expiration by those of the 

 trunk of insects b . He seems to have been led to the 

 adoption of this opinion* not so much by experiments 

 similar to that of Reaumur just stated, but by observing 

 that in many instances these two sets of spiracles differ 

 from each other, the latter having a convex and the for- 

 mer a concave mouth or bed c . In some cases, however, 

 for instance during flight, he supposes the spiracles 

 of the trunk may receive as well as emit the air d : he like- 

 wise is of opinion, and it seems not improbable, that by 

 means of these openings in the trunk, from the rush of 

 the superfluous air through them, insects produce those 

 sounds for which they are remarkable, as the humming 

 of bees and flies. In the former he thinks the sound is 

 produced by the pneumatic apparatus covered by the 

 ends of the collar; while in the latter he attributes it to 

 the spiracles in the metathorax behind the wings attended 

 by a poiser c . I incline, however, to M. Dufour's opi- 

 nion f , that the vocal spiracles in the Hymenoptera, as 

 well as in the Diptera, are those behind the wings. Per- 

 haps both theories may be right ; for if you take any 

 common humble-bee, you will find that, in the hand, it 

 produces one kind of sound when its wings are motion- 



a Mr. B. Clark thinks that he has discovered spiracles in this 

 larva in the usual situation, (Essay on the Bots, <SfC. 48. t. ii.jT. 3.) 

 but they are probably analogous to the spiraculiform tubercles of 

 CE. Ovis. Reaum. iv. 566. t. xxxv. 17 19. t. Vallisnieri (Espericnz. 

 $c. 136) notices them. Surlc Vol des Ins. c. i. 423. 



c Ibid. 454. and c. iv. 66. note 1. d Ibid. c. i. 453. 



c Ibid. 459, 456. f Ibid. 459. 



