Prick it with a needle and it contracts. It
recognizes its food even at a microscopic distance; it appears
therefore to feel and perceive. Perhaps we might say that it has a
mind and will of its own. It is safer to say that it is irritable,
that is, it reacts to stimuli too feeble to be regarded as the cause
of its reaction. It engulfs microscopic plants, and digests them in
the internal protoplasm by the aid of an acid secretion. It breathes
oxygen, and excretes carbonic acid and urea, through its whole body
surface. Its mode of gaining the energy which it manifests is
therefore apparently like our own, by combustion of food material.
[Illustration: 1. AMOEBA PROTEUS. HERTWIG, FROM LEIDY.
_ek_, ectosarc; _en_, endosarc; _N_, food particles;
_n_, 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.
Pages:
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64