nucleus; _cv_, contractile vesicle.]

It grows and reaches a certain size, then constricts itself in the
middle and divides into two. The old amoeba has divided into two
young ones, and there is no parent left to die, and death, except by
violence, does not occur. But this absence of death in other rather
distant relatives of the amoeba, and probably in the amoeba
itself, holds true only provided that, after a series of
self-divisions, reproduction takes place after another mode. Two
rather small and weak individuals fuse together in one animal of
renewed vigor, which soon divides into two larger and stronger
descendants. We have here evidently a process corresponding to the
fertilization of the egg in higher animals; yet there is no egg,
spermatozoon, or sex.

It is a little mass of protoplasm containing a nucleus, and
corresponds, therefore, to one of the cells, most closely to the
egg-cell or spermatozoon of higher animals. If every living being is
descended from a single cell, the fertilized egg, it is not hard to
believe that all higher animals are descended from an ancestor
having the general structure or lack of structure of the amoeba.

But is the amoeba really structureless? Probably it has an
exceedingly complex structure, but our microscopes and technique are
still too imperfect to show more than traces of it. Says Hertwig:
"Protoplasm is not a single chemical substance, however complicated,
but a mixture of many substances, which we must picture to ourselves
as finest particles united in a wonderfully complicated structure."
Truly protoplasm is, to borrow Mephistopheles' expression concerning
blood, a "quite peculiar juice." And the complexity of the nucleus
is far more evident than that of the protoplasm. Is protoplasm
itself the result of a long development? If so, out of what and how
did it develop? We cannot even guess. But the beginning of life may,
apparently must, have been indefinitely farther back than the
simplest now existing form. The study of the amoeba cannot fail to
raise a host of questions in the mind of any thoughtful man.

As we have here the animal reduced, so to speak, to lowest terms, it
may be well to examine a little more closely into its physiology and
compare it briefly with our own.

The amoeba eats food as we do, but the food is digested directly
in the internal protoplasm instead of in a stomach; and once
digested it diffuses to all parts of the cell; here it is built up