INTERNAL ANATOMY OF INSECTS. 71 



tion. This physiologist, having observed on the surface 

 of submerged insects numerous bubbles of air, concluded 

 that they had passed through the above orifices a : but 

 Bonnet found by various experiments carefully conduct- 

 ed, that this appearance was caused by air which ad- 

 hered to the skin and its hairs, and that when the access 

 of this was precluded by carefully moistening the skin 

 with water previously to immersion, this accumulation 

 of air-bubbles on its surface did not take place b . And 

 in a variety of instances he observed large ones issue 

 from all the spiracles, especially the anterior ones. These 

 bubbles sometimes were alternately emitted and absorbed 

 without quitting the spiracle c , and at others were darted 

 with force to the surface of the water, where they ap- 

 peared to burst with noise d . This author is of opinion 

 that the^rs^ and last pair of these organs are of most im- 

 portance to respiration e . Reaumur subsequently owned 

 that Bonnet's arguments had shaken his opinion f ; and 

 some observations of his own, with respect to the respi- 

 ration of the hot of the ox, go to prove that expiration 

 and inspiration are not by the same spiracles; for he found 

 that the air in this animal was expired by the eight little 

 lower orifices before mentioned , from which he clearly 

 saw the air-bubbles issue the upper one he conjectures 

 receives the air h . As the only communication that this 

 grub has with the atmosphere is by its posterior extre- 

 mity, it follows, reasoning from analogy, that the ante- 

 rior respiratory plates of Dipterous larvae, which may be 

 regarded as representing the spiracles of the trunk in 



a Reaum.i. 13G. " Bonnet (Euvr. iii. 39. c Ibid. 43. 



d Ibid. 50. Ibid. 69. ' De Geer ii. 117. 



e See above, n. 50. h Reaum. iv. 520. 



