modified by surgery; Dual basis for sex; Opposite-sex basis in every
individual; The Free-Martin cattle; Partial reversal of sex in man.


In Chapter I, the "immortality" of the protoplasm in the germ cells of
higher animals, as well as in simpler forms without distinct bodies, was
mentioned. In these higher animals this protoplasm is known as
_germplasm_, that in body cells as _somatoplasm_.

All that is really meant by "immortality" in a germplasm is continuity.
That is, while an individual may consist of a colony of millions of
cells, all of these spring from one cell and it a germ cell--the
fertilized ovum. This first divides to form a new group of germ cells,
which are within the embryo or new body when it begins to develop, and
so on through indefinite generations. Thus the germ cells in an
individual living to-day are the lineal descendants, by simple division,
of the germ cells in his ancestors as many generations, or thousands of
generations, ago as we care to imagine. All the complicated body
specializations and sex phenomena may be regarded as super-imposed upon
or grouped around this succession of germ cells, continuous by simple
division.

The type of body in each generation depends upon this germplasm, but the
germplasm is not supposed to be in any way modified by the body (except,
of course, that severe enough accidents might damage it). Thus we
resemble our parents only because the germplasm which directs our
development is a split-off portion of the same continuous line of germ
cells which directed their development, that of their fathers, and so on
back. This now universally accepted theory is called the "continuity of
the germplasm."