I HAVE, been careful to speak of the "appearance"
of cyclical evolution presented by living things; for,
on critical examination, it will be found that the
course of vegetable and of animal life is not exactly
represented by the figure of a cycle which returns
into itself. What actually happens, in all but the
lowest organisms, is that one part of the growing
germ (A) gives rise to tissues and organs; while
another part (B) remains in its primitive condition,
or is but slightly modified. The moiety A becomes
the body of the adult and, sooner or later, perishes,
while portions of the moiety B are detached and, as
offspring, continue the life of the species. Thus, if
we trace back an organism along the direct line of
descent from its remotest ancestor, B, as a whole,
has never suffered death; portions of it, only, have
been cast off and died in each individual offspring.

Everybody is familiar with the way in which the
"suckers" of a strawberry plant behave. A thin
cylinder of living tissue keeps on growing at its free
end, until it attains a considerable length. At

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