and Dilated Tracheae 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, which seems to be the 

 chief use for which the vesicles are developed. 



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