204 THE ENTOMOSTRACA OF EPPING FOREST.
Enemies, Parasites, and Diseases.
Some of the most important enemies of the Entomostraca
have been mentioned incidentally in the previous section. The
subject is, however, worth a little further consideration. Of
the invertebrate animals which prey directly upon them may be
mentioned the well-known fresh-water polypes (Hydra), some
aquatic worms (Nais, &c.), the Water-mites (nearly all species),
a few Rotifers (Asplanchna, &c.), and aquatic Insect larvae of all
kinds. One of the latter, a species of Chironomus, I believe,
constructs a rough kind of snare which may often be seen
covered with great numbers of Daphnia, &c., looking like so
many flies in a spider's web. The fresh-water shrimp (Gammarus)
and the water wood-louse (Asellus), together with some aquatic
beetles and various other invertebrates, have also from time to
time been reported as feeding upon Entomostraca. Their
vertebrate enemies are chiefly fishes, but frogs and newts, both in
the larval and adult stages, have been found feeding to some
extent upon them. Ducks and other water-loving birds also
destroy a certain number, but the extent of their ravages is
unknown.
But Entomostraca are not only exposed to the attacks
of animals, they have also to be careful of certain innocent-
looking plants called Bladderworts (Utricularia). Luckily for
our Epping Forest species these plants do not grow commonly
in the district, but it has been shown (71) that, in places where
they thrive, they destroy a very great number of Entomostraca
by imprisoning the latter in their bladders and finally digesting
them.
The parasites of the Entomostraca include both Ecto-
parasites and Endo-parasites. To the former belong some
Rotifers (Brachionus rubens, Proales daphnicola), which attach
themselves more especially to species of Daphnia, and many
Infusoria (Colacium, Epistylis, Cothurnia, Podophrya, &c), some of
which are to be found occasionally on nearly every species. In
addition to these animal parasites there are also various kinds
of Algae, and a number of very curious organisms, probably Fungi
(Amaebidium, &c.), but having affinities with the Algae, which are
now and then to be found attached to various species. The
internal parasites, which, on the whole, do not seem to be very
common among the Entomostraca, include various kinds of
Protozoa, more particularly Gregarina, Cysticerci of numerous