egg,
and has no other known function than that of a propeller. Its movement
has been studied and found to be about 1/8 of an inch per minute. Only
the head and neck enter the egg. This head consists almost entirely of
the nuclear material which is supposed to determine the characters of
the future individual.

The ovum or egg contributed by the mother is much larger--nearly round
in shape and about 1/120 of an inch in diameter. Besides its nucleus, it
contains a considerable amount of what used to be considered as "stored
nutritive material" for the early development of the individual.

In ancient times the female was quite commonly supposed to be a mere
medium of development for the male seed. Thus the Laws of Manu stated
that woman was the soil in which the male seed was planted. In the Greek
_Eumenides_, Orestes' mother did not generate him, but only received and
nursed the germ. These quaint ideas of course originated merely from
observation of the fact that the woman carries the young until birth,
and must not lead us to imagine that the ancients actually separated the
germ and somatic cells in their thinking.

A modern version of this old belief was the idea advanced by Harvey that
the ovum consisted of fluid in which the embryo appeared by spontaneous
generation. Loeuwenhoek's development of the microscope in the 17th
century led immediately to the discovery of the spermatozoon by one of
his students. At the time, the "preformation theory" was probably the
most widely accepted--i.e., that the adult form exists in miniature in
the egg or germ, development being merely an unfolding of these
preformed parts. With the discovery of the spermatozoon the
preformationists were divided into two schools, one (the ovists) holding
that the ovum was the container of the miniature individual, the other
(animalculists) according this function to the spermatozoon. According
to the ovists, the ovum needed merely the stimulation of the
spermatozoon to cause its contained individual to undergo development,
while the animalculists looked upon the spermatozoon as the essential
embryo container, the ovum serving merely as a suitable food supply or
growing place.

This nine-lived notion of male supremacy in inheritance was rather
reinforced than removed by the breeding of domestic animals in the
still more recent past. Attention has been focused on a few great males.
For example, the breed of American trotting horses all goes back