SCIENTIFIC NOTES. 
103 
press the blood in the wing vessels back towards the heart. Moreover, 
there is no evidence of muscular action in the wing during stiffening. 
I am disposed to think the process is probably one of coagulation and 
evaporation. I hope some other entomologists will make such obser- 
vations as may be possible towards the elucidation of the problem. — 
Francis J. Buckell. Aprils 1891. 
By pricking the wings of insects, when they are expanding, with a 
needle, I find that they always exude a greenish liquid, which soon 
hardens into a solid mass ; and I have always looked upon this liquid 
as the medium by which the wings were expanded, evaporation and 
coagulation completing the work. The “ opaque drop ” exuded by the 
insect after expansion, and noticed by Mr. Fenn, I look upon as the 
natural exudation of the insect, the difference in colour between the 
expanding liquid and the exudation is due to the fact that the insect, 
as often as not, exudes in the pupa case before leaving it. and the 
difficulty which I find in understanding how the liquid could find its 
way from the wings, change colour and be exuded by the insect, makes 
me hesitate in connecting the two phenomena. Is it not more natural 
to think that the “opaque drop” is only an excess of the insect’s excre- 
ment? Re the theory whether the blood only passes through the large 
nervures or is more diffused, I leave the settlement of this to others 
more experienced and observant than myself ; simply stating here that 
I am inclined to think the blood is diffused over all the wing, that it 
flows from the body through the vessels around the large nervures, and 
from thence is discharged into every part of the wing. Did Mr. Water- 
house operate upon a newly-expanded wing, or upon one which had 
had time to stiffen? Saccular dilatation I can only explain by the 
supposition of air sometimes being forced between the wing membranes 
and sometimes by an excess of blood. — W. Reid, Pitcaple. May, 1891. 
I have been interested in the microscopic anatomy of insects, and 
the question of the “ how ” of the expansion of the wings after the 
emerging of the imago, has never seemed clear to me. From the 
microscopic observations I have made, I make out that the spiral 
appearance of the air tubes in the wings is not visible in the unexpanded 
wing, it is not easy to see at times, even in the fully expanded tissue, 
but the expansion, as it takes place, is all in the direction of length, the 
breadth of the wing being built up, of course, of laterally expanded 
nervures. It has seemed to me that the penetration of the fluid blood 
of the insect into the tubes surrounding the air vessels has a great part 
to play in this springing open of the spiral air tubes. In the complete 
air tube there is a spiral space between each coil of the tube, the tube 
is elastic, and may be compressed under the microscope, it springs out 
again on being released ; may not the mere penetration of moisture be 
sufficient to determine the partial uncoiling of the air tubes, which are 
compressed in the unexpanded stage? — Gerard Smith, Upper 
Clapton, N.E. 
With regard to wing expansion, there appears to be no reason for 
supposing that the blood passes along the nervures, other than in the 
capillary vessels surrounding the central tracheal passage. That the 
wing consists essentially of two layers, and that a fluid passes evenly 
between them is beyond question. I have repeatedly noted that this is 
so, and have carefully observed and separated the membranes, during 
