and Dilated Tracheew in Insects. 423 
rations per minute. It then ceased for an instant, and slightly separated its 
elytra without elevating them, and began again to respire more rapidly. At 
first its respiration was slowly but gradually increased, until a few seconds 
before it attempted to expand its wings and to elevate itself upon them, when 
the acts of respiration became exceedingly rapid, and amounted to at least 
120 per minute. These were most rapidly performed, and were then suddenly 
arrested at the instant before it attempted to unfold the wings. During this 
increased respiration the abdomen of the insect was distinctly enlarged, and 
it was quite evident that this enlargement, and the expansion of its wings, 
were being effected by forced inspirations, and maintained by the expansion 
of the air-sacs over the whole body, and the communication of these with the 
tracheal vessels in the wings themselves. As however the wings had become 
stiffened and dried through many hours, it did not completely succeed in its 
attempts to escape, but only partially raised itself upon them. The results 
were nevertheless sufficiently satisfactory to prove to me that the respiratory 
organs became distended previous to the act of flight, as the entire body was 
distinctly enlarged; the effect of which enlargement, together with an in- 
creased evolution of heat in the body, as the result of increased respiration, 
must, of consequence, be to diminish the specific gravity of the insect, and 
thus, by lessening the degree of muscular force required to raise it on its 
wings, considerably augment its powers of locomotion, w which seems to be the 
chief use for which the vesicles are developed. 
VOL. XX. 3K 
