stages. The first and lower stage is the cytode, which consists merely
of a particle of plasson, or quite simple plasm. The second and higher
stage is the cell, which is already divided or differentiated into
nuclear matter and cellular matter. We comprise both kinds--the
cytodes and the cells--under the name of plastids ("formative
particles"), because they are the real builders of the organism.
However, these cytodes are not found, as a rule, in the higher animals
and plants; here we have only real cells with a nucleus. Hence, in
these tissue-forming organisms (both plant and animal) the organic
unit always consists of two chemically and anatomically different
parts--the outer cell-body and the inner nucleus.

In order to convince oneself that this cell is really an independent
organism, we have only to observe the development and vital phenomena
of one of them. We see then that it performs all the essential
functions of life--both vegetal and animal--which we find in the
entire organism. Each of these tiny beings grows and nourishes itself
independently. It takes its food from the surrounding fluid;
sometimes, even, the naked cells take in solid particles at certain
points of their surface--in other words, "eat" them--without needing
any special mouth and stomach for the purpose (cf. Figure 1.19).

Further, each cell is able to reproduce itself. This multiplication,
in most cases, takes the form of a simple cleavage, sometimes direct,
sometimes indirect; the simple direct (or "amitotic") division is less
common, and is found, for instance, in the blood cells (Figure 1.10).
In these the nucleus first divides into two equal parts by
constriction. The indirect (or "mitotic") cleavage is much more
frequent; in this the caryoplasm of the nucleus and the cytoplasm of
the cell-body act upon each other in a peculiar way, with a partial