The genus Daphnia is a small group of freshwater Entomostracous Crustacea, which has long been celebrated for possessing the power of reproduction without the intervention of the male, and for laying two different sorts of eggs. In both cases the eggs pass from the ovary into a space or receptacle between the carapace and the back of the animal. The carapace, according to Milne-Edwards, is an excessive development of an anterior, probably mandibular segment which encloses the whole of the posterior part of the body, which lies freely in it, as it were in a bivalve shell. This bivalve shell or carapace is wisely open below and behind, but is closed along the back, and as it forms there a regular arch, and does not follow the sinuous margin of the back of the animal, there is left between the back and the carapace an open space or receptacle, into which the eggs are laid, and in which they remain until the young Daphnia is sufficiently developed to be able to swim about by itself. This “receptacle” is freely open to the surrounding water, but the eggs are prevented from falling out by a tongue-like projection, developed evidently for that purpose from the back of the animal. When, however, the young are ready for exclusion, the mother has but to depress her abdomen, and they easily slip from the receptacle into the open water. Although both the common or agamic and the ephippial eggs are thus protected by the carapace or valves until they are hatched, there is this difference, that the agamic eggs are carried about by the animal, and shortly before the next shedding of the skin, the young which have in the meantime been hatched swim away; while for the ephippial eggs, part of the carapace is specialized into a pod-like or saddle-shaped box called the ephippium , in which, when the skin is changed, they remain for some time before being hatched.