Page:The Zoologist, 1st series, vol 1 (1843).djvu/302

274 and it seemed to be done for that very purpose. At all events, it had that effect; for after it had been twice or thrice repeated, it produced a small longitudinal slit in the skin of the back of the fly.

The slit, once produced, was speedily enlarged by continuing the motion of the wings; and the glossy chesnut back, beneath the external coat of a dull light brown colour, began to appear. The head was now much depressed, and the back curved and elevated in an equal degree; the motion of the wings ceasing at the same instant. The next part of the process seemed to be effected without difficulty or exertion. The slit extended, and the body of the insect, beginning with the highest part of the back between the wings, steadily emerged. The wings themselves, still in their horizontal position, were gradually drawn back, so that their anterior edges formed a continually decreasing angle with the sides, and at last became parallel with them. At this instant the head was freed, and raised aloft. Convulsive motions of the body and tail ensued, and presently, wings and legs were all released at once.

But there yet remained to be performed what seemed to be the most fatiguing and troublesome part of the operation, namely, the extrication and elongation of the whisks. Not one of these little Ephemeræ, previously to throwing off its envelope, had whisks exceeding of an inch in length;, I should think, was about the length of those of the majority. But after they had cast their skin, their whisks generally had been so much elongated as to measure an inch in length; and some even : those of a very few retained their pristine dimensions. As I have said, this part of the process was apparently more difficult than that which had preceded it. It was certainly more tedious; for in most cases it took up three or four times as much time, and frequently, even more than that: and in not a few instances, it was not completed at all, for the insect took flight with the husk still attached to its setæ.

It was while the Ephemera was striving to extricate its whisks that the benefit of having firmly fixed its feet to the substance which supported it (as above noticed) became apparent. All the force which the little fly could use seemed brought into requisition. The whisks were as unwilling to leave their sheaths, as an eel, in the hands of an unpractised person, its skin. Their perfect extrication, therefore, depended upon the skin of the feet retaining its hold: when it yielded, the exuviæ still adhered, and the flight of the insect was necessarily much impeded; for they all, without exception, took flight almost as soon as the operation was over. From the first appearance of the slit