These singular little creatures are found in stagnant fresh water: they
are very small, and, at first sight, appear like a bivalve shell. The
animal which is enclosed in this two-valved case, opens and shuts it
at will; when it does this, it throws out from one end of the shell
numerous whitish hair-like members; it is by moving these that it is
enabled to swim with considerable celerity, and it never stops until
it meets with some object on which it can rest. Its two antennæ, which
issue from the fore part of the shell, are long, very flexible, and
bent backwards; their articulations are numerous, which gives them
great freedom of motion. The movements of these antennæ contribute
materially to the swimming powers of the creature.
At the place where the head is united to the body, a small black point
is seen,—this is the eye of the animal.
[Illustration: _Cypris pubera._
(Fig. 1, highly magnified; fig. 2, natural size.)]
The Cypris changes its shell like the rest of the Crustacea; it is
found in marshes where vegetable substances are growing. Sometimes they
are so numerous, that the water appears covered with them; they are
more usually found in Spring and Autumn than at any other part of the
year; from this it is inferred that there are two broods in the course
of the year.
The drying up of marshes during the Summer heats, destroys immense
numbers every season. It appears, however, from observation, that in
this case, some of these tiny creatures manage to bury themselves in
the mud, where they hermetically close their shells, and remain in a
kind of dormant state, until rain or other causes have again filled the
marshes with water.
A species nearly allied to this, the _Artemia Salina_, the Lymington
shrimp, or brine-worm, is able to live in the brine of the salt-pans,
which is so strongly impregnated with salt, as to destroy any other
Crustaceous animal.
Myriads of these animalculæ are to be found in the salterns at
Lymington, in the open tanks or reservoirs, where the brine is
deposited previous to boiling. A pint of this brine contains about a
quarter of a pound of salt. These tanks are called clearers, as the
liquor becomes clear in them, an effect which the workmen attribute,
in some degree, to the rapid and continual motion of the brine-worm,
or the particles which cloud the liquor serving for its food; but this
is mere conjecture. So strongly persuaded, however, are the workmen of
this fact, that they are accustomed to transport a few of the worms
from another saltern if they do not appear at their own. They increase
astonishingly in the course of a few days.
It is observable that the brine-worm is never seen in the sun-pans,
where the brine is made by the admission of sea-water during the
Summer, and which are emptied every fortnight; but only in the pits and
reservoirs, where it is deposited after it is taken out of the pans,
and where some of the liquor constantly remains, when it becomes much
diluted with rain water. From October till May, (during which time the
manufacture is at a stand,) a few only of the worms are visible; but at
the approach of Summer, young ones appear in great numbers.