endoplastule. The protoplasm is more or less
extensively excavated by fluid spaces, vacuoles; one clearer circular
space or vacuole, which is invariably present, appears at intervals,
enlarges gradually, and then vanishes abruptly, to reappear after a
brief interval; this is called the contractile vacuole (c.v.). The
amoeba is constantly changing its shape, whence its older name of
the Proteus animalcule, thrusting out masses of its substance in
one direction, and withdrawing from another, and hence slowly
creeping about. These thrust-out parts, in its outline, are called
pseudopodia (ps.). By means of them it gradually creeps round and
encloses its food. Little particles of nutritive matter are usually to be
detected in the homogeneous protoplasm of its body; commonly
these are surrounded by a drop of water taken in with them, and the
drop of water is then called a food vacuole. The process of taking in
food is called ingestion. The amoeba, in all probability, performs
essentially the same chemical process as we have summarised in
Sections 10, 11, 12; it ingests food, digests it in the food vacuoles
and builds it up into its body protoplasm, to undergo kataboly and
furnish the force of its motion-- the contractile vacuole, is probably
respiratory and perhaps excretory, accumulating and then, by its
"systole" (compare Section 44), forcing out of its body, the water,
carbon dioxide, urea, and other katastases, which are formed
concomitantly with its activity. The amoeba reproduces itself in the
simplest way; the nucleus occasionally divides into two portions and
a widening fissure in the protoplasm of the animal's body separates
one from the other. It is impossible to say that one is the parent cell,
and the other the offspring; the amoeba we merely perceive, was one
and is now two. It is curious to note, therefore, that the amoeba is,
in a sense, immortal-- that the living nucleus of one of these minute
creatures that we examine to-day under a microscope may have
conceivably drawn, out an unbroken thread of life since the remotest
epochs of the world's history. Although no sexual intercourse can be
observed, there is reason to believe that a process of supposed
"cannabalism," in which a larger amoeba may occasionally engulph
a smaller one, is really a conjugative reproductive process, and
followed by increased vitality and division.

Section 52. Now if the student will compare Section 35, he will see
that in the whi