From the earliest times attention has been drawn to the enormous abundance of species of the family in certain localities. Johann Anton Scopoli, writing in the 18th century, speaks of them as so abundant in one place in Carniola that in June twenty cartloads were carried away for manure! _Polymitarcys virgo_, which, though not found in England, occurs in many parts of Europe (and is common at Paris), emerges from the water soon after sunset, and continues for several hours in such myriads as to resemble snow showers, putting out lights, and causing inconvenience to man, and annoyance to horses by entering their nostrils. In other parts of the world they have been recorded in multitudes that obscured passers-by on the other side of the street. And similar records might be multiplied almost to any extent. In Britain, although they are often very abundant, we have scarcely anything analogous. Fish, as is well known, devour them greedily, and enjoy a veritable feast during the short period in which any particular species appears. By anglers the common English species of _Ephemera_ (_vulgata_ and _danica_, but more especially the latter, which is more abundant) is known as the "may-fly," but the terms "green drake" and "bastard drake" are applied to conditions of the same species. Useful information on this point will be found in Ronalds's _Fly-Fisher's Entomology_, edited by Westwood. Ephemeridae belong to a very ancient type of insects, and fossil imprints of allied forms occur even in the Devonian and Carboniferous formations. There is much to be said in favour of the view entertained by some entomologists that the structural and developmental characteristics of may-flies are sufficiently peculiar to warrant the formation for them of a special order of insects, for which the names Agnatha, Plectoptera and Ephemeroptera have been proposed. (See HEXAPODA, NEUROPTERA.) BIBLIOGRAPHY.--Of especial value to students of these insects are A. E. Eaton's monograph (_Trans. Linn. Soc._ (2) iii. 1883-1885) and A. Vayssière's "Recherches sur l'organisation des larves" (_Ann. Sci. Nat. Zool._ (6) xiii. 1882 (7) ix. 1890). J. A. Palmén's memoirs _Zur Morphologie des Tracheensystems_ (Leipzig, 1877) and _Über paarige Ausführungsgänge der Geschlechtsorgane bei Insekten_ (Helsingfors, 1884), contain important observations on may-flies. See also L. C. Miall, _Nat. Hist. Aquatic Insects_ (London, 1895); J. G. Needham and others (New York State Museum, Bull. 86, 1905). (R. M'L.; G. H. C.)