indistinguishable from the common amoeba.)

If you touch one of these creeping amoebae with a needle, or put a
drop of acid in the water, the whole body at once contracts in
consequence of this mechanical or physical stimulus. As a rule, the
body then resumes its globular shape. In certain circumstances--for
instance, if the impurity of the water lasts some time--the amoeba
begins to develop a covering. It exudes a membrane or capsule, which
immediately hardens, and assumes the appearance of a round cell with a
protective membrane. The amoeba either takes its food directly by
imbibition of matter floating in the water, or by pressing into its
protoplasmic body solid particles with which it comes in contact. The
latter process may be observed at any moment by forcing it to eat. If
finely ground colouring matter, such as carmine or indigo, is put into
the water, you can see the body of the amoeba pressing these coloured
particles into itself, the substance of the cell closing round them.
The amoeba can take in food in this way at any point on its surface,
without having any special organs for intussusception and digestion,
or a real mouth or gut.

The amoeba grows by thus taking in food and dissolving the particles
eaten in its protoplasm. When it reaches a certain size by this
continual feeding, it begins to reproduce. This is done by the simple
process of cleavage (Figure 1.17). First, the nucleus divides into two
parts. Then the protoplasm is separated between the two new nuclei,
and the whole cell splits into two daughter-cells, the protoplasm
gathering about each of the nuclei. The thin bridge of protoplasm
which at first connects the daughter-cells soon breaks. Here we have
the simple form of direct cleavage of the nuclei. Without mitosis, or
formation of threads, the homogeneous nucleus divides into two halves.