Save that it is curious that while the larvæ of some species are carnivorous those of others are vegetarians, there is nothing very remarkable about what may be called the infantile period. But when this is ended the span of life remaining to them as adults is brief indeed. Instinctively realizing that the time of transfiguration is at hand, the erstwhile crawling grub rises to the surface of the stream, and almost in the twinkling of an eye it mounts into the air on gauzy wings, there for a brief space to execute an aerial dance which in its every phase is amazing. Some species never see the sun. They emerge as the sky begins to redden, and as its glory fades they, too, expire. This brief space is all that Nature has allowed them in which to fulfil her behest to all living things—to increase and multiply. And myriads die without even a chance to effect this consummation of existence. The dance is a Dance of Death, and it is performed by a host so vast as to surpass the bounds of belief save to those who have had the good fortune to witness a scene so amazing. D’Albertis tells of a gathering which he witnessed on the Fly River, New Guinea—for these insects have a world-wide distribution—wherein countless myriads were assembled. “For miles the surface of the river, from side to side, was white with them as they hung over it on gauzy wings; at certain moments, obeying some mysterious signal, they would rise in the air and then sink down anew like a fall of snow.” And in this assemblage he estimated that there was but one female to every five or six thousand males. It is during this flight that the act of mating is performed. The fortunate male from the host of rivals, in this mid-air embrace is aided by the foremost pair of legs, which are especially curved to effect this purpose. The embrace is momentary. Thereafter he dies; to the female a somewhat longer span of life remains, for she has yet to deposit her eggs, and this being done _en masse_, she, too, expires. It is curious that these creatures, which in their winged state have never seen the sun, should be attracted by light. But such is the case. I well remember witnessing an instance of this years ago, while staying, one August, at Bingen on the Rhine. Dinner was served in the open air, and just as the soup was served May-flies in myriads swarmed round the lamps and fell on the tables as thick as snow-flakes. Some of these were in copula, and I succeeded in bottling a few specimens for the British Museum, where they still remain to remind me of this amazing scene. About three hundred species of May-flies are known, and some enjoy a somewhat longer span of life than others. In no case, however, do they emerge till just before sunset; but in some species it is believed life may be prolonged for as much as three or four days, or even longer, if the weather be cold and wet, so as to keep them in a state of enforced rest, which amounts to a state of coma.