our
children. We may also furnish our children an environment which will
stimulate their desire and lend opportunity for similar or greater
advancement than our own. This is _social inheritance_, or the product
of _environment_--easy to confuse with that of _heredity_ and very
difficult to separate, especially in the case of mental traits.

It will likewise become clear as we proceed that there is no mechanism
or relationship known to biology which could account for what is
popularly termed "pre-natal influence." A developing embryo has its own
circulation, so insulated from that of the mother that only a few of the
most virulent and insidious disease germs can ever pass the barrier. The
general health of the mother is of utmost importance to the vitality,
chances of life, constitution and immunity from disease of the unborn
child. Especially must she be free from diseases which may be
communicated to the child either before or at the time of birth. This
applies particularly to gonorrhoea, one of the most widely prevalent as
well as most ancient of maladies, and syphilis, another disastrous and
very common plague which is directly communicable. As to "birthmarks"
and the like being directly caused by things the mother has seen or
thought about, such beliefs seem to be founded on a few remarkable pure
coincidences and a great deal of folk-lore.

Reproduction in its simplest form is, then, simply the division of one
cell into two parts, each of which develops into a replica of the
original. Division is also the first stage in reproduction in the most
complicated animal bodies. To get an idea of what takes place in such a
division we must remember that a cell consists of three distinct parts:
(a) the protoplasm or cytoplasm, (b) the nucleus, and (c) a small body
known as the centrosome which need not be discussed here.

When a cell division takes place, the nucleus breaks up into a number of
thread-like portions which are known as chromosomes. There are supposed
to be 24 pairs, or 48, in the human cell. All the evidence indicates
that these chromosomes carry the "factors" in inheritance which produces
the characters or characteristics of the individual body.

In mitosis or ordinary cell division, these chromosomes split
lengthwise, so that the new cells always have the same number as the
original one. When the germ-cells of the male and female make the
division which marks the first step in reproduction, however, the