440 
CRUSTACEA. 
and two-jointed tarsus. From the front of the head arise two very short, single-jointed antennse. The shell is so 
transparent that ail the viscera may be seen through it. The matrix, when tilled with eggs, occupies the major 
part of its interior ; but their number, even in the most numerous broods, does not 
exceed ten. The eye is the first part of the animal which makes its appearance whilst 
in the egg. The abdomen is terminated by a long tail suddenly folded back. The 
animal always swims on its back or sides, giving to its antennae and legs quick and 
repeated motions, and executing, with the greatest ease, all kinds of evolutions. It is 
subject, in its infancy, to the disease alluded to more in detail under Daphnia, named 
the Ephippium (la Selle) ; but the Ephippium is always of a determinate shape. Kept 
Fig. 19.— Po^phemus stagiiorum, confinement, it soon dies ; and its young do not live long after their first moultings. 
Jurine was not able to detect males amongst the individuals he examined, but the 
species is rare near Geneva. It is, however, very common in the ditches and lakes of the north of France, [as well 
as in England], where it may often be seen in considerable troops. 
[Evadne, Loven, mSwed. Trans., 1835, differs from Polyphemus in having the head not detached from the body, 
with the antennae (or mandibular palpi, according to Loven) bifid. E. Nordmanni. Found in the Baltic Sea.] 
Daphnia, Muller, has the antennae as long as the body, divided into two branches, of which the posterior is 
4-jointed, the basal joint being very short ; and the anterior is 3-jointed. The eye forms a small point, and is 
not accompanied, except in a few species, by an anterior black dot, mistaken by Muller and Ramdohr for a second 
eye in Lynceus. Although of such minute size, the anatomy of these animals has been elaborately investigated 
by Schaffer, Ramdohr, Strauss, and the elder Jurine, — Strauss having especially examined their structure, whilst 
Jurine closely noticed their habits. The mouth is situated beneath, at the base of the rostrum. We consider as 
an elongated clypeus the inferior portion of the head, termed labrum by Strauss, and we apply the name of 
labrum to the part which he term! the posterior lobule of the labrum. Beneath this are two very strong mandi- 
bles destitute of palpi, and applied against two horizontal maxillae, terminated by three strong corneous spines, 
like recurved hooks. Then succeed ten legs, all of which have the second joint vesiculose ; the eight anterior 
terminated in a fin-like dilatation, with bearded filaments at its edges, arranged like a crown ; the two anterior 
appear more especially organs of prehension. Ramdohr calls them palpi, and Jurine, hands, (as in Cyclops) ; from 
the bearded terminal setae, we do not see why they should not be employed in respiration*, although Strauss has 
a different opinion. The two hind-feet have a somewhat different form. The abdomen or body is divided into 
eight segments, perfectly disengaged within the shell, long, slender, and bent down at the tip, which is termin- 
ated by two recurved hooks. The sixth segment has a row of tubercles, and the fourth a kind of tail. The eggs 
remain in a large dorsal sac or matrix, between the shell and the body, for some time after they are discharged 
from the ovaries. Muller gave the name of Ephippium (la Selle) to a long, dark-coloured spot, which at certain 
seasons appears after the moulting of the females at the upper part of the valves of the shell, and which Jurine 
attributes to a disease. According to Strauss, this Ephippium consists of two external plates, riveted on the back 
by a hinge, and inclosing two oval capsules, each formed of two valves or lateral plates. Each of these capsules 
incloses a corneous, greenish egg, similar in other respects to the common eggs, but remaining much longer un- 
hatched, and passing the winter in this state, the Ephippium forming a defence at the time of moulting : this 
Ephippium and its eggs are cast, and the eggs produce young, agreeing precisely with those of the ordinary eggs. 
The eggs, according to Jurine, hatch in summer in two or three days, but they are capable of remaining for a very 
long time in a state of desiccation. "Wlien the young, which have attained considerable developement in the ma- 
trix of the female, are fit to be discharged, the parent suddenly deflexes the tail and they quit the pouch. [Want 
of space prevents us from giving numerous details relative to the gradual developement of the young.] The males 
are very different from the females ; the head shorter, the rostrum less extended, the valves of the shell nar- 
rower and less gibbose, the antennse much larger. Strauss was unable to detect the sexual organs of this sex. The 
two valves of the shell terminate in both sexes in a style, toothed on its under-side, curved near its base, and of a 
length equal to that of the valves. At each moulting, however, this style becomes shorter, so that in adult indi- 
viduals it forms merely an obtuse point. A single act of impregnation is sufficient for several succeeding (six at 
least) generations, as proved by Jurine. About eight days after their birth, the young moult for the first time, 
and repeat the operation every five or six days, according to the state of the weather : not only the body and the 
valves, but also the branchiae, and the setae of the oars, cast off their epidermis. It is not until the third moult- 
ing that they begin to produce young, and at first they only lay a single egg, then two or three, the number 
gradually increasing to as many as fifty-eight in one species (D. magna). The following day after laying her 
eggs, the female moults, and in the shed teguments the shells of the eggs of her last brood are also found. The 
eggs of each brood are alniost exclusively of one sex, it being very rare to find two or three males in a female 
brood, 'and vice versa. In five or six broods in the summer, one at least is of males. These Crustacea cease to 
breed and to moult at the approach of winter, and are killed by the first frost. The Ephippial eggs which had 
been laid in the summer hatch in the following spring, and in a short time the ponds or ditches are again peopled 
with an infinity of Daphnice. Many naturalists have attributed the red colour of some of these waters to the 
I>resence of myriads of D.pidex ; but Strauss has never proved this fact, the species being generally but slightly 
coloured. In the morning and evening, and even in cloudy days, the Daphnise generally station themselves on 
the surface, but in the heat of the day they seek the depths of the water. They swim by taking short springs. 
* Strauss indeed considered Cypris and Cythere not to be real Bran- 
cliiopods, because their feet are not branchial ; but we do not see 
why the hairs of the two anterior and of the antenna; may not, as well 
as those of the palpi and anterior maxillae, perform the office of 
branchiae. 
