SOIENTTFIC 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 tho problem. — 

 Francis J. Buckell. April, 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 



