420 LIFE-HISTORY OF LESTES LED A SELYS, 



was marvellously rapid, so that, almost before I could realize it, 

 the wing had i*eached its full length, and practically also its 

 perfect shape, except for a small region near the pterostigma. 

 Here were two large indentations at the side of the wing, 

 separating a portion which was destined to become the pterostigma 

 itself. Turning my attention to this, I noticed a series of small 

 indentations along the costa, each one representing a future 

 postnodal. These soon disappeared, leaving only the two large 

 indentations mentioned before. The latter gradually stretched 

 themselves out, becoming less and less concave, and as 

 they did so the isolated portion between them began to harden 

 and to appear as a distinct and regular plate: this being due to 

 the closing up and uniting of the numerous trachea? surrounding 

 it. It appeared that these trachea? or fluid-tubes combined 

 naturally in pairs simply by the stretching of the wing, and that 

 as soon as a pair approached one another and lay exactly parallel, 

 a membranous hardening took place around them and they 

 closed up into a strong and distinct nervure. 



It thus appears that the nodus and the pterostigma are the two 

 points at which the development of the wing was arrested, so to 

 speak. This appears to be due to the excessive number of trachea? 

 at these points, the quicker development of the adjacent parts 

 causing the large indentations which were so noticeable. But 

 when the arrested development became completed, it would of 

 course be natural to expect a great strengthening and extra 

 stability of those very parts. This we find to be the case, the 

 nodus and stigma being in a very true sense the supports or 

 points about which — next to the base itself — the wing is built. 



Immediately after full expansion the wings appear flabby and 

 weak, and are of a pale greenish colour, the pterostigma being 

 slightly paler. In the course of an hour or so the greenish tint 

 almost entirely disappears, the wings becoming brilliantly hyaline 

 and the pterostigma deepening into a pale brown. Adaj^ or two 

 afterwards the wings are perfectly stiff and transparent, the 

 pterostigma being opaque and dark brown. The insect is 

 capable of weak flight an hour or two after the complete develop- 

 ment of the wings. 



