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 theirs/ 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 or, 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 
loiaer orifices before mentioned g , from which he clearly 
saw the air-bubbles issue — the upper one he conjectures 
receives the air K 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 CEuvr. iii. 39— . c Ibid. 43. 
" Ibid. 50. ■ Ibid. G9. f De Geer ii. 117. 
c See above, p. 50. h Reaum. iv. 520. 
