oth consist of matter of a nitrogenous
nature.

When we examine a simple cell, we find we can distinguish morphological
parts. In the first place, we find in the cell a round or oval body
known as the nucleus. Occasionally the nucleus is stallate or angular;
but as a rule, so long as cells have vital power, the nucleus maintains
a nearly constant round or oval shape. The nucleus in its turn, in
completely developed cells, very constantly encloses another structure
within itself--the so-called nucleolus. With regard to the question of
vital form, it cannot be said of the nucleolus that it appears to be an
absolute essential, and in a considerable number of young cells it has
as yet escaped detection. On the other hand, we regularly meet with it
in fully-developed, older forms, and it therefore seems to mark a higher
degree of development in the cell.

According to the view which was put forward in the first instance by
Schleiden, and accepted by Schwann, the connection between the three
co-existent cell-constituents was long thought to be of this nature:
that the nucleolus was the first to show itself in the development of
tissues, by separating out of a formative fluid (blastema,
cyto-blastema), that it quickly attained a certain size, that then fine
granules were precipitated out of the blastema and settled around it,
and that about these there condensed a membrane. In this way a nucleus
was formed about which new matter gradually gathered, and in due time
produced a little membrane. This theory of the formation of the cell is
designated the theory of free cell formation--a theory which has been
now almost entirely abandoned.

It is highly probable that the nucleus plays an extremely important part
within the cell--a part less connected with the function and specific
office of the cell, than with its maintenance and multiplication as a
living part. The specific (animal) function is most distinctly
manifested in muscles, nerves, and gland cells, the peculiar actions of
which--contraction, sensation, and secretion--appear to be connected in
no direct manner with the nuclei. But the permanency of the cell as an
element seems to depend on nucleus, for all cells which lose their
nuclei quickly die, and break up, and disappear.

Every organism, whether vegetable or animal, must be regarded as a
progressive total, made up of a larger or smaller number of similar or
dissimilar cells. Just as a tree constitutes a mass arran