IN DAPHNIA, AND OF THE STEUCTUEE OP THE EPHIPPIUM. 
83 
tion of the agamic eggs in the receptacle, but I have several times observed the state of the 
ovary within a few minutes after this took place. The ovary was then as distinct as usual : 
it consisted of a slightly undulating tube, varying in the middle from ’0033 to '005 in 
width, but contracted at both ends, where also the walls became fainter, so that neither 
the anterior nor the posterior termination could be observed. The anterior contracted part 
appeared to be empty, or at least a few irregular curved hues only were visible. Nearly 
opposite to the hind end of the heart was generally an elliptic ovarian mass, with a 
constriction in the centre of the upper margin, and containing from two to four, or at 
most five cells, each consisting of a large, perfectly circular nucleus, surrounded by 
the cells, which formed a sort of narrow border to it. The nucleus can sometimes 
scarcely be distinguished, but is usually slightly darker than the ovarian mass itself, 
and this latter than the cells. This ovarian mass occupies the whole width of the 
ovary, and is followed in a linear series by three or four more, all very similar to the 
first, all with the lower margin regularly arched, the upper constricted at or near to 
the centre. The longer axes of these ovarian masses, which is in the direction of the 
longer axis of the body, is about -0058 in length, the shorter ’0033 : the diameter of the 
cells varies from -001 to -0004. After the first three or four, the masses become smaller, 
two or more are abreast, and the walls gradually more indistinct: the cells also are 
usually smaller behind, but not regularly so, often a mass with large cells behind one 
with small ones. In many cases, however, the order of arrangement is not so regular, 
nor the masses so distinct; but they appear, as it were, heaped together, and even where 
the ovary is at first as described above, it gradually changes to this latter appearance. On 
all sides of the ovary are often scattered ch’crdar cells, containing each one or more oil- 
globules, but they are most numerous at the downward bend of the abdomen. A few 
hours, or sometimes immediately, after the deposition of the agamic eggs in the receptacle 
between the back and the shell, it usually happens that at the posterior part of the 
ovary one of the above-mentioned cells swells a little, and becoming surrounded by brown 
granules, may be called a germinal vesicle (Plate VI. fig. 2 g'). Other cells, sometimes two 
or three in number, but usually only one, are at first visible in the ovarian mass, but 
gradually disappear. The contents of this mass continue to grow darker, until it comes 
to resemble Plate VI. fig. 3 g ' after this they generally either fade away, or break 
up into more or less compact little balls (Plate VI. fig. 8) which gradually disappear. 
The ephippial egg in these early stages differs from the corresponding state of agamic 
eggs in the determinate position and number, being never more than one on each side 
of the body ; and in the constant absence of the large oil-globules, which are constantly 
present, and show themselves very early in the latter form of eggs. 
This embryonic ephippial egg may generally be met with in those specimens which 
have recently moulted and laid their eggs, and indeed I should say that the cases in 
which it is not produced are quite exceptional, probably not more than one in five or six. 
I have traced the progress of it in thirty-three instances, and in thirty it gradually 
disappeared again as described above; in the other three the dark granules increased 
