STATES OF INsECrs. (dmago.) 293 
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 of an aqueous fluid into these or- 
gans 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*. Swammerdam, who ap- 
pears to have been the first physiologist that paid atten- 
tion to this subject, was of opinion that an aériform as 
well as an aquiform fluid contributes to produce the ef- 
fect 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 pel- 
lucid globules, becoming insensibly drops—which he con- 
cluded proved the action of the latter; and he noticed, 
also, that the wings were furnished with trachez, which 
were at that time distended by the injected air; whence 
he justly surmised, that the action of the azr was also of 
* Reaum. i. Mem. ult. De Geer i. 73. Swamm. Bibl. Nat. i. 184. 
M. Carus (Introd. to Comp. Anat. ii. Append. No. 2. 394.) observed 
the course of this temporary circulation in the wing of Agrion Puella. 
The excurrent (or arterial) stream took its course along the inner 
margin of the wing, and the recurrent (or venous) returned along the 
outer, whilst occasionally other transverse currents took their course 
through the net-work of the wing, from its inner to its outer margin. 
As the wings were further developed the circulation in them gradu= 
ally became weaker and ultimately ceased. 
