250 
CUUSTACliA. 
tail *. The ovaries are situated alonf? tlie sides between this segment 
and the first, and opi'n separately near the baek into a cavity — matrix, 
J urine — formed lietwixt the shell and tlie body, in which the ova 
remain for some time after they are produced. 
Muller has given tlie name of ephippium, or saddle, to a large, 
oliscure, and rectangular spot, which at certain periods and particu- 
larly in summer, ajipears, after the females have changed their 
tegument, on the superior part of the valves of the shell, and which 
he attributes to disease. According to Straus this ejihippium pi’c- 
sents two oval, dia])hanous ampullae, placed one before the otlier, and 
forming with those of tlie opposite side two small oval capsules, 
ojiening like that of a bivalve. Jt is divided, as are also the valves of 
wliich it forms a part, into two lateral halves, united by a suture 
along their superior edge ; its interior exhibits another similar, but 
smaller one, with free edges, provided it be not the superior that is 
attached to the valves, the two halves of which, playing upon each 
other as if hinged, present the same ampulla; as the exterior lids. Each 
capsule contains an egg with a greenish and liorny shell, otherwise 
similar to an ordinary ovum, but recpiiring a greater length of time 
for its dev(!lopement, and being destined to pass the winter in statu quo. 
When the animal is about to change its tegument, tlie ejihippium, as 
well as its ova, is abandoned with the exiivicje, of which it consti- 
tutes a part, and which protect them during the winter from the 
cold. The heat of spring hatches them, and young Daphniae are 
[iroduced exactly similar to those which come from the ordinary eggs. 
Scha*tfer affirms that they will remain for a long period in a desiccated 
state without losing the vitality of the germ, but none of those pre- 
served in that condition by Jurine were ever hatched. They are en- 
tirely free, or do not adhere to each other in their peculiar cavities. 
Jn summer, according to .Jurine, they may be hatched in two or 
three days. In the climate of Paris, where Straus observed them at 
all jieriods of the year, they require at least one hundred hours. The 
foetus, twenty-four hours after the jiroduction of the ovum, is a mere 
rounded and unformed mass, on which, when closely examined, may 
be seem obtuse rudiments of arms in the form of very short and im- 
licrfect stumps glued to the body ; neitluir head nor eye is pcreejitible ; 
and as yet, the green or reddish body dotted with white, like the egg, 
exhibits no motion. It is only at the nineteenth hour, and when the 
hour has appeared, and the arms and valves are elongated, that the 
foetus begins to move. Jiy the hundredth hour it is very active, and 
finally, at the hundred and tenth it only differs from the newly hatched 
animal in the seta; of the oars which are still glued to their stem, and 
in the tail of the valves which is bent under and received between 
their inferior edges. Towards the end of the fifth day, the tail, which 
terminatc's the valves in the young animal, and the seta; of the arms 
become free, and the feet for the first time begin to move. The 
young being ready to make their appearance, the mother lowers her 
* Wc omit various details of the organization, because some ean only he com- 
])ichcnded by means of drawings, and others ajiiuar conimun to most of the llran- 
cbioiioda. 
