THE ENTOMOSTRACA OF EPPING FOREST. 199
vast number of facts, some of which, there is good reason to
believe, will be found to be either directly or indirectly of
importance to our own well-being.
Reproduction and Development.
Although this is evidently not the place to enter into a
lengthy account of the reproduction and development of the
Entomostraca, a few points may be usefully touched upon, as
they furnish the explanation of some of the peculiarities in the
records from Epping Forest to be discussed presently. The
first of these is that the vast majority, if not all the fresh-water
Entomostraca, possess the power of parthenogenetic reproduc-
tion. Among the Cladocera and many of the Ostracoda this
power is put into operation regularly for a certain period or
periods each year. The length of the purely parthenogenetic
period varies very considerably in different species, but appears
in the main to depend rather upon the individual idiosyncrasy
of the species than directly upon external influences (107). It
may be confined to the first generation, i.e., the one hatching
from the resting eggs, as in Moina, or it may run through four or
five generations, as in some forms of Daphnia, Chydorus, &c., or
again it may extend to many generations, as in most of the
limnetic species of the Cladocera. In some few instances,
Bosmina longirostris (?) and most species of Cypris, the partheno-
genetic may even be the only method of reproduction. The
species of Copepoda and the remainder of the Ostracoda, on the
other hand, while still retaining the potentiality of a sexual
reproduction, are usually represented at all times by individuals
of both sexes.
Another fact to be noticed is that all the Cladocera are
capable of producing two kinds of eggs, namely, the ordinary
eggs, known usually as "summer-eggs," not needing ferti-
lisation, but fitted only for immediate development under
the protection of the mother, and "resting - eggs," or,
as they are sometimes termed, "winter - eggs," capable
of remaining undeveloped for very long periods, many
years in some cases, but requiring fertilisation. The appear- 
ance of these two kinds of eggs is very different, and the resting-
eggs, moreover, are, in most cases, provided with a special
covering formed from the shell of the mother and known in its
most highly evolved state as an "ephippium." Females
carrying resting-eggs, with or without a true "ephippium," are