196 THE ENTOMOSTRACA OF EPPING FOREST.
subject of local distribution is by no means thoroughly under-
stood at present, and requires much further investigation.
Corresponding to their wide range in space, we also find a
very great variety in the habitats of the Entomostraca. Indeed,
it may be stated generally, that wherever there is water, there
will be found some representatives of the group. It matters not
whether the water is in large or small quantities, whether hot or
cold, whether clean or dirty. Little temporary pools, and some-
times cart-ruts and hoof-prints, yield their contingent as well as
the largest lakes. Even in situations where there is no standing
water at all, as in some bogs, damp mossy hollows, and mosses
on tree trunks above the water's edge, some species are sure to be
found if carefully searched for. But perhaps the most curious
natural situation in which Entomostraca have been found is that
mentioned by Fritz Muller, who discovered in Brazil a species
of ostracod living in the cups formed by the leaves of plants
belonging to the Order Bromeliaceae. The animals appeared to
be quite at home, and, what is still more remarkable, they did not
resemble any of the species found in the ponds and other waters
of the surrounding country.
Habits of the Entomostraca.
The study of the habits of the various species offers a wide
field for very useful work, as comparatively little is yet known
on this most fascinating subject. The facts hitherto elucidated
have been for the most part connected merely with the modes of
life exhibited by the different forms. From this point of view
the Entomostraca fall pretty naturally into two divisions,
swimmers and non-swimmers. The swimmers again may be
divided into the constant and the intermittent swimmers. The
former, confined to a comparatively small number of species of
Cladocera and Copepoda, are best represented by the pelagic,
limnetic, or plankton forms, i.e., those which live continuously
in the open water of fair-sized ponds or lakes. These forms
may support themselves in the water either entirely by virtue of
their powerful organs of locomotion e.g., Diaphanosoma, Diaptomus,
Cyclops strenuus, &c., or they may possess long spines and other
outgrowths increasing their power of remaining suspended
without much effort, e.g., Daphnia cucullata, Bosmina, Bythotrephes,
&c. The group of the constant swimmers also includes all the
species of the genera Daphnia and Ceriodaphnia not already
included among the plankton forms, for although some of these