52 
POPULAR SCIENCE REVIEW. 
daphniae, and they are rather numerous in species. The harp- 
shaped lynceus, being very clear and transparent, is well 
adapted for giving a good idea of the whole family. 
There remains another group of freshwater Entomostraca to 
he mentioned. This is the family Cyprididce .* The animals 
of this large family are remarkably similar in appearance (at first 
sight) to a small bivalve shell ; and indeed, when dried, have 
often been mistaken for small molluscs. 
The body is contained entirely within the carapace, which is 
formed of two valves, open in front, and attached to each other 
at the back by a sort of ligamentous hinge. They have only 
two or three pairs of feet, which, when the animal moves 
through the water, or creeps on the surface of the mud or 
leaves of aquatic plants, are protruded through the open front 
of the shell. This shell the animal can open or shut at 
pleasure, and being rather thick and opaque, the little creature 
can withdraw itself completely from view, as well as protect 
itself from all its minor enemies ever ready to attack it. The 
cyprides are to be found in every pond or ditch where the 
water remains stagnant, and sometimes in immense numbers. 
They are not so prolific as the four-horned water-fleas, already 
mentioned, but in some of the larger species we can count as 
many as twenty-four eggs in a single individual. As in the 
Cyclopidse and Daphnise, a single impregnation lasts the animal 
for life, as well as all its successive generations. The mother 
deposits her eggs upon some such bodies as the leaves of 
aquatic plants, and frequently various individuals combine to fix 
on the same spot a mass of eggs, consisting of several hundreds. 
In about four or five days, these eggs are hatched, and the young 
come forth already covered with a shell, and having the appear- 
ance of the perfect animal. They seem to excel all the other 
Entromostraca in being able to stand the influence of drought. 
When the ponds and ditches in which they live become dried 
up in summer, they bury themselves in the mud as long as it 
retains any moisture, and may be found active as ever imme- 
diately the rain falls and again overflows their habitations. 
These little creatures appear to enjoy a very lively and active 
existence in their native element. Instead of being fixed to 
one spot, and condemned to live in comparative darkness, like 
the mussels and other molluscous animals which they resemble 
in external appearance, they can open their shelly valves at 
pleasure, “ enjoy the light and move about at their will, some- 
times burying themselves in the mud, and at others darting 
through the water, the humid element of their sphere. If they 
meet any unforeseen object, they conceal themselves at once 
* Legion, Lophyropoda • order, Ostracoda. 
