It has been mentioned, that, in the case of the dragon-fly, the completion of the unfolding of its wings occupies about a quarter of an hour, but that sometimes it is even half an hour. The ordinary period is from five to ten or fifteen minutes in most insects, but it is sometimes prolonged to an hour, or to several hours. Again, in others, as we have already seen in the history of the emergence of the gnat, and other insects, from their aquatic state in the pupa, it is completed in a few seconds, and the insect only rests for this brief period on the surface of the water, previous to taking flight from its apparently somewhat dangerous position.
Some observations of Mr. Rennie show, in a singular manner, the fact before mentioned, that if the wings, while yet wet and soft, are in any way pressed upon, or otherwise injured, they will never assume their proper appearance. "The thread by which a chrysalis is suspended may sometimes snap asunder; when this happens, and the chrysalis is allowed to remain, it will not usually produce an insect complete in all its parts; for the side upon which it lies being pressed against an unyielding substance by its own weight, instead of hanging lightly suspended by a silken cord, is prevented from becoming duly expanded, and when the insect is excluded, it is found to be deformed. A colony of the brown-tail moth, which we reared during the summer of 1829, spun in the corner of a nurse-box, a common web of several chambers for containing the pupæ. One of these chambers being accidentally torn, a pupa fell upon the earth in the bottom of the box, and in due time, a female moth was produced from it; but she never succeeded in expanding her wings, which remained till her death, shrunk, rumpled, and totally useless for the purpose of flying, though in every other respect she was full grown, and deposited in the box a group of fertile eggs, covered with down from her tail, as neatly as was done by her sisters of the same brood. In the summer of 1825, the chrysalis of a small tortoise-shell butterfly, (_Vanessa urticæ_,) lost its hold of its silken suspensory, and fell upon the pasteboard bottom of a nurse-box, resting in a sort of angular position, so that the case of the upper wing on the left side, pressed upon the box with the whole weight of the chrysalis above it. When the butterfly made its appearance, it expanded its wings as usual; but the wing upon which it had rested was not half the size of the one on the right side which had lain uppermost. Another of the same brood had, from some cause, not grown so large in the caterpillar state as the rest. It was transformed, notwithstanding, into a chrysalis, which appeared healthy and well-formed; but when the butterfly appeared, though it did not differ from the usual appearance, its wings never expanded a single hair's breadth, and remained always in the same state as when it issued from the chrysalis."