But the above is not the only state of Ephemerids, for their entire existence really lasts a year. Linnæus has thus summed up the total life of these little creatures: "The larvæ swim in water; and, in becoming winged insects, have only the shortest kind of joy, for they often celebrate in a single day their wedding, parturition, and funeral obsequies." The eggs, in fact, give birth to more or less elongated larvæ, which are always provided with three filaments at the end of the abdomen, and which breathe the oxygen dissolved in the water by tracheo-branchiæ along the sides of the body. They are carnivorous, and live on small animal prey. The most recent authors who have studied them are Mr. Eaton, in England, and Mr. Vayssiere, of the Faculte des Sciences, at Marseilles. _A propos_ of the larvæ of Ephemera or May-flies, we must speak of one of the entomological rarities of France, the nature and zoological place of which it has taken more than a century to demonstrate. Geoffroy, the old historian of the insects of the vicinity of Paris, was the first to find in the waters of the Seine a small animal resembling one of the Daphnids. This animal has six short and slender thoracic legs, which terminate in a hook and are borne on the under side of the cephalic shield. This latter is provided above with two slender six-jointed antennæ, two very large faceted eyes at the side, and three ocelli forming a triangle. The large thoraceo-abdominal shield is hollowed out behind into two movable valves which cover the first five segments of the abdomen (Fig. 1). The last four segments, of decreasing breadth, are retractile beneath the carapax, as is also the broad plume that terminates them, and which is formed of three short, transparent, and elegantly ciliated bristles. These are the locomotive organs of the animal, whose total length, with the segments of the tail expanded, does not exceed seven to eight millimeters. The animal is found in running waters, at a depth of from half a meter to a meter and a half. It hides under stones of all sizes, and, as soon as it is touched, its first care is to fix itself by the breast to their rough surface, and then to swim off to a more quiet place. It fastens itself so firmly to the stone that it is necessary to pass a thin knife-blade under it in order to detach it. [Illustration: FIG. 1.--LARVA OF MAY FLY. (Magnified 12 times.)]