IN DAFHNIA, AND OF THE STEUCTIJEE OP THE EPHIPPITJM. 
85 
“ and there spreading, forms the ephippium.” Professor Huxley compares the ephippium 
with the outer coat of the winter egg of Lacinularia, which is a product of the ovary. 
Prof. Milne-Edwaeds says*, “ On voit alors (vers la fin de I’ete) se former dans la cavite 
o\’ifere, a la face interne de chaque valve, une lame opaque, qui constitue bientot un 
appareil particuher, auquel on a donne le nom ephippium. II consiste en deux battans 
semblables aux valves de la carapace, dont chacun est garni interieurement dune ou de 
deux petites ampoules, transparentes, disposees de fa9on a former avec leur congenere 
deux petites capsules bivalves,” &c. In this description it is said that the ephippium is 
formed of two valves, like those of the carapace, whereas they are in truth a part of the 
carapace, and each valve is said to be provided internally with two small transparent 
“ ampoules,” which are, however, merely places where the valves are pushed outwards 
in order to leave the necessary space for the two eggs. 
Even Prof. OwExf, in his very interesting Lectures, has described the ephippium as an 
opaque layer, “ developed on the inner sui’face of the common incubating cavity,” and 
neither he, nor, so far as I know, any other naturalist, has explained the homologies of 
the “ inner valve,” or the limitation of the ephippial eggs to two. 
I have already described the gradual development of the ephippial egg, until it forms 
an elongated, dark, homogeneous mass (Plate VI. fig. 10. Plate VII. fig. I) occupying appa- 
rently the whole of the ovary, which at least cannot elsewhere be seen. I have watched 
the process in three specimens : one unfortunately died, but in the other two I was able 
to observe the subsequent growth. 
At the above stage the receptacle was in both cases occupied by young, nearly ready 
for exclusion ; when this was effected, the only trace of the ephippium was a slight 
redness in the receptacle. This gradually increased, especially along a bow-shaped line 
(Plate VII. fig. Ip) very like the caustic which an ordinary teacup throws on the liquid 
contained in it. 
This hne and the accompanyirrg redness is formed by a local alteration of the valve, 
the line being the upper part of the above-mentiorred outbowings in which the two eggs 
wiU eventually be placed, but the darkening gradually extends until a saddle-shaped 
piece (Plate VII. fig. 6), of the form described by Steauss, is distinguished from the rest 
of the shell by the darker colour and the smaller size of the cells. 
In the meantime the two eggs have left the ovary and deposited themselves in the two 
ampullae provided for them. On the 27th of July last, at 5 o’clock in the” afternoon, I 
was so fortunate as to witness this process. I was looking through my compourrd micro- 
scope at a specimen like Plate VII. fig. I, when suddenly the hind part of the dark ovarian 
mass turned up along the line {m) and elongated considerably. The animal was quite 
quiet, but the dark matter glided in two streams slowly and steadily into the ephippium, 
and when there, in a few seconds contracted to less than half its previous length, at the 
same time becoming oval, and thus forming the two ephippial eggs. The vitelline 
membrane must, at this period, be very elastic to admit of such alterations of shape. 
* Hist. Nat. des Crustacees, vol. iii. p. 377. t Lectures on Invertebrate Animals, p. 324. 
MDCCCLVII. N 
