That their hold on life during this final stage of existence is brief there can be no gainsaying, for it is passed fasting. Jaws are wanting, and the whole alimentary canal has been transformed into one long air-chamber. Its walls are now of extreme tenuity, and by changes in the interior of the tube, valves are formed which convert the stomach into a capacious air-sac.” When movements,” remarks Dr. David Sharp, “tend to increase the capacity of the body cavity then air enters into the stomachic sac by the mouth orifice, but when muscular contractions result in pressure on the sac they close the orifices of its extremities by the valve-like structures just referred to; the result is, that as the complex movements of the body are made the stomach becomes more and more distended by air.” It was known even to the old naturalists that the dancing May-fly is a sort of balloon, but they were not acquainted with the exact mode of inflation. Palmen says that in addition to the valve-like arrangements we have described, the entry into the canal is controlled by a circular muscle with which are connected radiating muscles attached to the walls of the head. The canal thus strangely transformed performs the functions of a balloon, and at the same time aids the functions of the reproductive organs. Where vast numbers of individuals set out simultaneously to achieve their nuptials there would seem to be no need for special devices on the part of either sex to call attention to their whereabouts. Nevertheless, it is highly probable that the female exhales some distinctive odour; otherwise, having regard to the fact that she is overwhelmingly outnumbered by suitors, her discovery in such a crowd would be impossible, and it is of vital importance that no time should be lost in effecting conjugation, for the time for its accomplishment is perilously short. But there is another possible means of discrimination—the males may distinguish the females by the very different appearance of the head in the latter. At any rate, this may be true of some species wherein the males have no less than seven eyes, and these of three different kinds! The compound eyes, characteristic of insects, are, in these, divided, one half being set upon the summit of a pillar raised high above the level of the head, the other part remaining in its normal place at the side of the head; and in front of these, on what may be called the forehead, are three separate simple eyes, or “ocelli.” A reference to Plate 32, Fig. 3, will make this clear.