THE ENTOMOSTRACA OF EPPING FOREST.
265
As was pointed out in the Wanstead Park paper, the
Cladocera reach their maximum development, as regards
number of species, in September, and their minimum in
January, whilst the otherwise fairly steady rise from the latter
month to the former is interrupted by a marked reduction in
August. The supposed retrogression in March has not been
confirmed. As regards the Ostracoda the facts seem to show
that there are two maxima—namely, one in early spring (March),
which is the larger, and one in early autumn (September). Of
the two minima, that in August is much lower than that in
January. The Copepoda do not exhibit very much variation
during the year from the point of view of the number of species,
but the figures given suggest that there may be, as in the case
of the Ostracoda, two maxima—namely, one in spring (April),
and the other in early autumn (September). These maxima
are practically equal in intensity. The two minima are also
nearly equal, but that in the summer (July and August) is some-
what smaller than that in the winter (January).
Comparative abundance of the different species.
The question of the comparative abundance of various
species—i.e. of the rare and common forms, is certainly one that
deserves more attention than it has hitherto received. When
dealing with the lower forms of animal life, and especially with
the fresh-water forms, which are notorious for their wide distri-
bution, it is not always possible to obtain good evidence of