foUR freshwater entomostraca. 47 
process is not peculiar to these water-fleas, but is common to 
most of the Crustacea, it is yet so easily observed that it be- 
comes extremely interesting to watch it. It is one which in 
early life is all-important to the existence of the creature, as by 
the time it casts its shell the body has increased in size, and 
thus it requires a new and larger habitation. Even in the ma- 
ture state, it seems to be necessary for the animal’s wellbeing. 
Living for the most part in water which abounds in the parasitic 
freshwater Polyzoa, Confervse, &c. the shell of the daphnia soon 
becomes overgrown with these organisms, which intrude them- 
selves even into the interior of their carapace, thus materially 
impeding the poor creature’s motions and ultimately destroying 
its life. 
The changes which the young undergo in their progress to 
maturity are equally interesting to the observer of their habits 
and manners. The mother is ovo-viviparous ; the eggs, as soon 
as they leave the ovary, take their place in an open space on the 
back, where they remain quite free and unattached till the time 
of expulsion. In general, about the end of the fifth day, these 
eggs are hatched, are tolerably well developed, and are then 
launched into open day. These young differ but little in form 
from their parents, except in the smaller development of their 
parts (figs. 7, 8). When first expelled, the young have a long 
spine at the extremity of their shell ; this, however, at first is 
curled up within the shell, and it is not till they have been in 
the water for a few seconds, and begun to move about, that this 
tail suddenly, and with a jerk, springs out and assumes its 
natural position. The hairs of the large-branched antenna may 
be seen to spring forth in the same sudden manner, being pre- 
viously folded up along the stem. In a short period after its 
birth, the young animal is exactly like its parent, gradually in- 
creasing its size, and casting its shell as it grows, till it assumes 
the perfect state of the mature daphnia. 
The species of water-fleas belonging to the Daphniadcc , 
hitherto described as British, are about fourteen or fifteen in 
number, and may be met with in similar situations as the 
Daphnia pulex. 
In the same haul of the net as this in which we have found 
the branched-horned water-flea, we find another entomostracon 
perfectly different in shape and appearance from the last, and 
possessed of four large horns or antennse. This is the Four- 
horned, or smaller. Water-flea, the Cyclops quadricornis * 
(figs. 11,12). _ _ 
The history of this little creature is equally interesting as the 
preceding. The body of the animal is enclosed within a horny 
* Legion, Lopbyropoda ; order, Copepodct ; family, Cyclopidce. 
