And the germ-cells (eggs and spermatozoa) of volvox are
immortal like the protozoa. But, 2, there are nutritive, somatic
cells, which nourish and transport the germ-cells, and after their
discharge die. These somatic cells, being mortal, differ altogether
from the germ-cells and the protozoa. The protoplasm must differ in
chemical, or molecular, or other structure in the two cases, and we
distinguish the germ-plasm of the germ-cells, resembling in certain
respects Naegeli's idioplasm, from somatoplasm, which performs most
of the functions of the cell. The somatoplasm arises from, and hence
must be regarded as a modification of, the germ-plasm. The
germ-plasm can increase indefinitely in the lapse of generations,
increase of the somatoplasm is limited.
When a new individual develops, a certain portion of the germ-plasm
of the egg is set aside and remains unchanged in structure. This,
increasing in quantity, forms the reproductive elements for the next
generation. The germ-plasm, which does not form the whole of each
reproductive element, but only a part of the nucleus, is thus an
exceedingly stable substance. And there is a just as real continuity
of germ-plasm through successive generations of volvox, or of any
higher plants or animals, as in successive generations of protozoa.
In certain plants there is an underground stem or rootstock, which
grows perennially, and each year produces a plant from a bud at its
end.
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