SUBORDINATED TO, BUT COORDINATED WITH, the large ovum. The nuclei of
the two cells, as the vehicles of the hereditary features of the
parents, are of equal physiological importance. In some cases we have
succeeded in proving that the mass of the active nuclear substance
which combines in the copulation of the two sexual nuclei is
originally the same for both.

These morphological facts are in perfect harmony with the familiar
physiological truth that the child inherits from both parents, and
that on the average they are equally distributed. I say "on the
average," because it is well known that a child may have a greater
likeness to the father or to the mother; that goes without saying, as
far as the primary sexual characters (the sexual glands) are
concerned. But it is also possible that the determination of the
latter--the weighty determination whether the child is to be a boy or
a girl--depends on a slight qualitative or quantitative difference in
the nuclein or the coloured nuclear matter which comes from both
parents in the act of conception.

The striking differences of the respective sexual cells in size and
shape, which occasioned the erroneous views of earlier scientists, are
easily explained on the principle of division of labour. The inert,
motionless ovum grows in size according to the quantity of provision
it stores up in the form of nutritive yelk for the development of the
germ. The active swimming sperm-cell is reduced in size in proportion
to its need to seek the ovum and bore its way into its yelk. These
differences are very conspicuous in the higher animals, but they are
much less in the lower animals. In those protists (unicellular plants
and animals) which have the first rudiments of sexual reproduction the
two copulating cells are at first quite equal. In these cases the act