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IV.—The Modifications which the Egg of the | Hooded-eyed| 
~ Medusa undergoes before Fecundation. By M. A. Grarp. 
WE may take as a type the egg of Rhizostoma Cuviert. This 
medusa is found in great abundance, during autumn, along the 
shore of Wimereux, along with Chrysaora hyoscella and some 
other Acalephs. 
The smallest eggs in the ovary are formed of a transparent 
vitellus, enclosing a germinal vesicle and a nucleolus. One does 
not recognize any enveloping membrane at this stage. In pro- 
portion as the ovum increases in size, its transparency diminishes. 
The vitellus is charged with deutoplasm, and the germinal vesicle 
becomes more indistinct; at the same time one may distinguish on 
the periphery a very delicate vitelline membrane closely applied 
,against the vitellus. At a further stage the egg presents on its 
surface a series of spherules equally spread over the whole. These 
are filled with a perfectly transparent substance, and are separated 
from the external membrane by a thin layer of granular proto- 
plasm, identical with that which occupies the centre and covers 
over the germinal vesicle. An optical section of the egg may then 
be compared roughly with that of a young vegetable stem at the 
moment the first circle of vascular bundles appears, which then 
divides the parenchyma into three parts: one central, one peri- 
pheral, and a third radial, uniting the two. The hyaline spherules 
rapidly increase till they touch each other, and at the same. time 
they attack the vitellne membrane. With a slight magnification 
it seems as if the vitellus was surrounded by a layer of cells which 
projected from its surface at right angles. More highly magnified 
one sees that the central granular protoplasmic mass is connected 
with the vitelline membrane by an immense series of little columns 
widened at both their extremities like the stalactitic columns we 
sometimes find in a cavern, uniting the two masses of stalagmite, 
that of the ceiling and that of the floor. These columns are con- 
stituted of a protoplasm less granular than that of the interior of 
the ovum. Finally, at the moment when the egg arrives at matu- 
rity, the columns break and leave only very slight thicknesses of 
the vitelline membrane at their former points of attachment. Then 
we have a central granular mass in which the germinal vesicle is 
not directly observable, and around this mass a transparent zone, 
which separates it from the vitelline membrane. 
Professor Harting has seen in the eggs of Cyanea Lamarekii 
and C. capillata the stage in which the columns appear,* but not 
* Harting, “Notices Zoologiques” (‘ Niederlandisches Archiv,’ Band [r, 
Heft IIL). 
