this stage to the stage of complete development a satisfactory series
of embryos has now been collected, but it is impossible to give here,
even in outline, a description of the evolution of the human embryo.
No one can understand this intricate subject without the aid of
diagrams, models, and other material beyond the reach of all save
laboratory workers.

By the end of the second month the development of the embryo has
advanced so far that anyone could recognize its human shape. About
that time, too, the external sexual organs make their appearance. At
first these are quite similar in both sexes; and, if they are used as
the criterion, it is possible only toward the end of the third month
to say whether the embryo is a male or female.

THE DETERMINATION OF SEX.--The fact that a number of months pass
before the sex can be distinguished by an external examination of the
fetus has led to the erroneous belief that it can be influenced
during the early part of pregnancy or actually determined at will.
Various means to accomplish this have been suggested; many of them
depend upon modifying the mother's mode of living according as a boy
or girl is desired. The most widely known of these doctrines, that of
Schenck, was to the effect that the sex of the offspring is always
that of the weaker parent. He suggested, therefore, that increasing
the vigor of the mother by an appropriate diet would produce a male
child, whereas a decrease in her strength would lead to the opposite
result. His views, however, were incorrect. After studying extensive
statistics Newcomb came to the conclusion that "it is in the highest
degree unlikely that there is any way by which a parent can affect
the sex of his or her offspring."