Their Collection and Investigation. 51
unassisted eye, but had a diameter or total length of as much
as from the one-tenth to the half of an inch. The inhabitants
of these relatively large tree-like or sac-shaped fabrications
in no case yielded a greater measurement than the l-4000th
or the 1-3000th part of an English inch, so that the number
included in the larger aggregates is almost beyond calculation.
The student must by no means confine himself to the
collection and examination of water-plants in his search for
Infusoria. Innumerable forms are to be met with growing
upon other aquatic animals : insect larvae, molluscs, and the
more minute Crustacea, yielding an abundance of different
forms, their "fluffy" appearance, as seen with the naked
eye or with the aid of a lens, being a sure sign of the presence
of the required organisms. The little Entomostracan—
Cyclops—may be more especially mentioned as commonly
supporting on its body and limbs a perfect forest-like growth
of infusorial types, including, it may be, representatives of
each of the three primary sections referred to in my earlier
observations. In this manner the class Ciliata is usually
typified by one or more species of Epistylis; that of the
Flagellata by Cephalothamnium and Deltomonas; while that of
the Tentaculifera may be represented by one or two species
of Podophrya; and all of which Infusoria, as so far known,
are obtained under no other conditions.
Although ponds, ditches and other expansions of water
may be recommended to the student as his first area of
exploration, these represent but one out of numberless
sources from whence Infusoria are to be derived. A multitude
of species are essentially parasitic, living within the intestinal
viscera of higher animals. Many terrestrial insects, worms,
and molluscs, discharge the duty of hosts to special varieties.
The frog, in common with other Amphibia, supports quite an
abundant infusorial fauna, consisting of both ciliate and
flagellate types ; while even the higher Vertebrata, including
horses, sheep, oxen, and man himself, are not exempt from
infusorial dependents.2
2 [An article descriptive of the chief varieties of parasitic Infusoria has
been contributed by the author to the 'Popular Science Review' for 1880,
p. 293.—Ed.