gies remain incapable of
development. It results that such energies, remaining virtual, have no
practical importance.

In an analogous sense we may say that all the cells of the body are
hermaphrodite, as all germinal cells, for each possesses in itself the
undifferentiated energies of each sex. Each spermatozoid contains all
the energies of the paternal and maternal ancestry of man, and each
egg those of the paternal and maternal ancestry of woman. The male and
the female are only the bearers of each kind of germinal cells
necessary for conjugation, and each of these bearers only differs from
the others by its sexual cells and by what is called correlative
sexual differences. But we must not forget that the germinal cells
themselves are only differentiated at a certain period in the
development of the embryo; they are thus hermaphrodite originally and
only become male and female later.

New experiments made on the eggs of sea urchins and other organisms
have shown that conjugation may be replaced by an external irritating
agent; for example, the action of certain chemical substances is
sufficient to make eggs develop by parthenogenesis which would have
died without this action. An entire being has been successfully
produced from an egg divided into two by means of a hair. And even
from the protoplasm of the egg without its nucleus, with the aid of a
spermatozoid. We must not, however, base premature hypotheses on these
facts.

When a female cell, or egg, develops without fecundation
(parthenogenesis) its nucleus enlarges and divides in the same manner
as conjugated nuclei (mitosis).

A point of general interest is what is called the _specific
polyembryony_ of certain parasitic insects (hymenoptera of the genus
_Encyrtus_). According to _Marchal_, their eggs grow and divide into a
considerable number of secondary eggs, each of which gives rise to an
embryo and later on a perfect insect. By shaking the eggs of certain
marine animals they have been caused to divide into several eggs
and thus to produce several embryos. All the individuals arising from
the division of the same egg of _Encyrtus_ are of the same sex.

[Illustration: PLATE I

CELL DIVISION

FIG. 1. Cell before division.
FIG. 2. Division of centrosome.
FIG. 3. Formation of chromosomes.
FIG. 4. Dissolution of nucleus.
FIG. 5. Lining up of chromosomes.
FIG. 6. Division of chromosomes.
FIG. 7. Division of chromosomes.
F