The winter-eggs usually go through the early stages of segmentation within a short time after they are laid, but after this a longer or shorter period of quiescence occurs, during which the eggs may be dried or frozen without injury. The sides and floor of a dried-up pond are often crowded with ephippia, containing winter-eggs which develop quickly when replaced in water; and the resting-stage of winter-eggs produced in aquaria can often be materially shortened by drying the ephippia which contain them, though such desiccation does not appear to be necessary for development. Under normal conditions large numbers of winter-eggs remain quiescent through the winter and hatch in the following spring. The individual developed from a sexually fertilised winter-egg is invariably a parthenogenetic female: the characters of the succeeding generations differ in different cases. In a few forms, of which _Moina_ is the best known, the parthenogenetic female, produced from a winter-egg, may give rise to males, to sexual females, and to parthenogenetic females, so that the cycle of forms which intervene between one winter-egg and the next is short. A sexual female produces one or two winter-eggs, and if these are fertilised they are enclosed in an ephippium and cast off; if, however, the eggs when ripe are not fertilised, they atrophy, and the female produces parthenogenetic eggs, being thenceforward incapable of forming sexual “winter” eggs. An accidental absence of males may thus lead to the occurrence of parthenogenesis in the whole of the second generation. The regular production of sexual individuals in the second generation from the winter-egg appears to depend on a variety of circumstances not yet understood. Mr. G. H. Grosvenor tells me that _Moina_ from the neighbourhood of Oxford may give rise to several successive generations of parthenogenetic individuals, when grown in small aquaria. In the greater number of Daphniidae, the parthenogenetic female, produced from a winter-egg, gives rise only to parthenogenetic forms, and it is not until after half a dozen parthenogenetic generations have been produced that a few sexual forms appear, mixed with the others. Such sexual forms are fairly common in April or May in this country; they produce “winter” eggs and then die, the generations which succeed them through the summer being entirely parthenogenetic. In late autumn sexual individuals are again produced, giving rise to a plentiful crop of winter-eggs, but many parthenogenetic females are still found, and some of these appear to live and to reproduce through the winter. In _Sida_, in the Polyphemidae and Leptodoridae, and in most of the Lynceidae, sexual individuals are produced only once in every year, while in a few forms which inhabit great lakes the sexual condition occurs so rarely that it is still unknown.