294 STATES OF INSECTS. 



the tubes, and being impelled into their minutest ramifi- 

 cations, necessarily expands their folds ; for the nervures 

 themselves are folded, and as they gradually extend in 

 length with them, the moist membranes attached to them 

 are also unfolded and extended. In proportion as this 

 takes place, the expanding membranes approach each 

 other, and at last, being dried by the action of the atmo- 

 sphere, become one. To promote this motion of the fluid, 

 seems the object of the agitations which the animal from 

 time to time gives to its unexpanded wings. That a kind 

 of circulation, or rather an injection of an aqueous fluid 

 into these organs, actually takes place, may be ascertained 

 by a very simple experiment. If you clip the wings of a 

 butterfly during the process of expansion, you will see 

 that the nervures are not only hollow, but that, however 

 dry and empty they may subsequently be found, they at 

 that time actually contain such a fluid a . Swammerdam, 

 who appears to have been the first physiologist that paid 

 attention to this subject, was of opinion that an aeriform 

 as well as an aquiform fluid contributes to produce the 

 effect we are considering. He had observed that, if a 

 small portion be cut off from the wing of a bee, a fluid of 

 the latter kind exuded from its vessels in the form of 

 pellucid globules, becoming insensibly drops — which he 

 concluded proved the action of the latter ; and he no- 

 ticed, also, that the wings were furnished with tracheae, 

 which were at that time distended by the injected air ; 

 whence he justly surmised, that the action of the air was 

 also of great importance to produce the expansion of the 

 wing b . And Jurine found that every nervure contains 



a Reaum. i. Mem. ult. De Geer i. 73. Swamm. BM. Nat. i. 184. 

 b Swamm. Ihid. 



