41
THE OVUM AND
nucleus of the yelk-cell ? If the former, it is in all probability
the most essential rudiment of the embryo ; but if it be the
nucleus of the yelk-cell its importance vanishes with the forma¬
tion of the yelk-cell, and according to the analogy of most
cell-nuclei, it must either become absorbed altogether at a
subsequent period, or continue for a time simply rudimentary,
without forming any important new structure. The follow¬
ing is the ordinary career of a simple cell : a nucleus is
present in the first instance ; around it a cell is formed ; the
nucleus at first often increases in size as the cell grows, but
their growth is by no means proportionate, that of the cell
being much more rapid ; the cell-contents are at first transpa¬
rent ; a firm precipitate or new formation next commences in
the cell, and this occurs immediately around the nucleus,
which is at first enclosed by it ; the nucleus then either
becomes entirely absorbed, or continues only rudimentary and
(with the following exception) I have never observed it to
give origin to any other essential formation. One or more
oil-globules once appeared to me to be formed during the ab¬
sorption of the nucleus in the adipose cells within the cranial
cavity of a young carp. The importance of the decision of
this question in reference to the germinal vesicle thus becomes
very obvious. Unfortunately, however, neither the observa¬
tions upon the subsequent relations of the germ-vesicle, nor
those on the origination of the ovum, are sufficiently extensive
or certain for the purpose.
We shall next proceed to analyse both views of the question
more minutely, and afterwards compare them with the obser¬
vations. If the germ-vesicle be a young cell, in the first place,
it is absolutely necessary that the yelk-cell should first exist,
and that the germ-vesicle should afterwards be developed within
it; 2dly, the germ-vesicle must not be connected with the
vitelline-membrane, but must be developed free at some chosen
spot within the cavity of the yelk; 3dly, the germ-vesicle
may be regarded either as a cell without a nucleus, and in
that case the spots of Wagner belong to the cell-contents, or
Wagner’s spot, when it is single, is the nucleus ; when there
are several present, the others either differ essentially from one
particular spot, and pertain to the cell-contents, or they are
nuclei of young cells afterwards to be developed within the