I. THE PROBLEM DEFINED

What is sex? A sexual and mixed reproduction. Origin of sexual
reproduction. Advantage of sex in chance of survival. Germ and body
cells. Limitations of biology in social problems. Sex always present in
higher animals. Sex in mammals--the problem in the human species.
Application of the laboratory method.

II. SEX IN TERMS OF INTERNAL SECRETIONS

Continuity of germ plasm. The sex chromosome. The internal secretions
and the sex complex. The male and the female type of body. How removal
of sex glands affects body type. Sex determination. Share of the egg and
sperm in inheritance. The nature of sex--sexual selection of little
importance. The four main types of secretory systems. Sex and sex
instincts of rats modified by surgery. Dual basis for sex. Opposite sex
basis in every individual. The Free-Martin cattle. Partial reversal of
sex in human species.

III. SEX AND SEX DIFFERENCES AS QUANTITATIVE

Intersexes in moths. Bird intersexes. Higher metabolism of males.
Quantitative difference between sex factors. Old ideas of
intersexuality. Modern surgery and human intersexes. Quantitative theory
a Mendelian explanation. Peculiar complication in the case of man.
Chemical life-cycles of the sexes. Functional-reproductive period and
the sex problem. Relative significance of physiological sex differences.