INTERNAL ANATOMY OF INSECTS. 71 
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*.. 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®, and at others were darted 
with force to the surface of the water, where they ap- 
peared to burst with noise®. ‘This author is of opinion 
that the first and last pair of these organs are of most im- 
portance to respiration’. Reaumur subsequently owned 
that Bonnet’s arguments had shaken his opinion*; and 
some observations of his own, with respect to the respi- 
ration of the bot of the ox, go to prove that expiration 
and inspiration are not by thesame 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. As the only communication that this 
grub has with the atmosphere is by its posterzor extre- 
mity, it follows, reasoning from analogy, that the ante- 
rior respiratory plates of Dipterous larvee, which may be 
regarded as representing the spiracles of the trunk in in- 
sects in general, are destined for the escape of the air, 
after it has parted with its oxygen, received by the anal 
ones’. So that there seems very good ground for 
@ Bonnet Giuvr. i. 39—. » Thid. 43. © Lbid. 50. 
4 Jbid. 69. © De Geer ii. 117. 
£ See above, p. 50. & Reaum. iv. 520. 
h Mr, B. Clark thinks that he has discovered spiracles in this 
larva in the usual situation, (Essay on the Bots, §c. 48. 1. lief: 3.) 
but they are probably analogous to the spiraculiform tubercles of 
CE. Ovis. Reaum. iv. 566. £. xxxv.17—19. t. Vallisnieri ( Hsperienz. 
&c. 136) notices them. 
