Bauhaus-Universität Weimar

Microscopical researches into the accordance in the structure and growth of animals and plants
Schwann, Theodor Schleyden
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


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