c. Liable to partial or complete upset in the very early stages;

d. Probably quantitative--stronger in some cases than in others.

The new definition is, then, really a combination and amplification of
the three older points of view.

The term "sex determination" does not mean to the biologist the changing
or determining of the sex at will on the part of the experimenter. This
might be done by what is known as "selective fertilization" artificially
with only the kind of sperm (X or Y as to chromosomes) which would
produce the desired result. There is as yet no way to thus select the
sperm of higher animals. It has been authoritatively claimed that
feeding with certain chemicals, and other methods to be discussed later,
has affected the sex of offspring. These experiments (and
controversies) need not detain us, since they are not applicable to the
human species.

Let us consider this fertilized egg--the contributions of the father and
the mother. The total length of the spermatozoon is only about 1/300 of
an inch, and 4/5 of this is the tail. This tail does not enter the 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