dification. We need not
deny that such laws and influences may have acted in the manner
suggested, but what we do deny is that they could possibly escape from
the ever-present and all-powerful modifying effects of variation and
natural selection.[212]

_Weismann's Theory of Heredity._

Professor August Weismann has put forth a new theory of heredity founded
upon the "continuity of the germ-plasm," one of the logical consequences
of which is, that acquired characters of whatever kind are not
transmitted from parent to offspring. As this is a matter of vital
importance to the theory of natural selection, and as, if well founded,
it strikes away the foundations of most of the theories discussed in the
present chapter, a brief outline of Weismann's views must be attempted,
although it is very difficult to make them intelligible to persons
unfamiliar with the main facts of modern embryology.[213]

The problem is thus stated by Weismann: "How is it that in the case of
all higher animals and plants a single cell is able to separate itself
from amongst the millions of most various kinds of which an organism is
composed, and by division and complicated differentiation to reconstruct
a new individual with marvellous likeness, unchanged in many cases even
throughout whole geological periods?" Darwin attempted to solve the
problem by his theory of "Pangenesis," which supposed that every
individual cell in the body gave off gemmules or germs capable of
reproducing themselves, and that portions of these germs of each of the
almost infinite number of cells permeate the whole body and become
collected in the generative cells, and are thus able to reproduce the
whole organism. This theory is felt to be so ponderously complex and
difficult that it has met with no general acceptance among
physiologists.

The fact that the germ-cells _do_ reproduce with wonderful accuracy not
only the general characters of the species, but many of the individual
characteristics of the parents or more remote ancestors, and that this
process is continued from generation to generation, can be accounted
for, Weismann thinks, only on two suppositions which are physiologically
possible. Either the substance of the parent germ-cell, after passing
through a cycle of changes required for the construction of a new
individual, possesses the capability of producing anew germ-cells
identical with those from which that individual was developed, or _the
new germ-c