The essential part of the cells, namely
the nuclei, coalesce into one nucleus, and an active process of cell
division and multiplication is at once started. The single cell divides
into two daughter cells, then again into four, and so on. Very early in
development, the cells, which at first appear similar, become
differentiated into different types, but the whole ordered sequence of
the development of an embryo is achieved by this cell division and
multiplication. Each original cell contains a substance which, on
account of its being easily colorable with artificial stains, is called
chromatin, and this chromatin is believed to be the bearer of the
hereditary qualities. The cell division is so arranged that each new
cell receives an equal share of the male and female chromatin, and this
process is continued in every case of cell division, so that
eventually, in every part of our bodies, the dual inheritance remains
complete.
But though both parents have thus an equal share in the cellular
elements of the new life, it is the female whose reproductive organs
provide for its nourishment and protection until birth takes
place.
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