Too much stress cannot be laid upon the point that such animal data, carefully checked up with the human material, cannot safely be used for any other purpose than to discover what the facts are about the human body.  When the discussion of human social institutions is taken up in Part II, the obvious assumption will always be that these rest upon human biology, and that we must not let our minds wander into vague analogies concerning birds, spiders or crustacea.

BIBLIOGRAPHY FOR CHAPTER I

1.  Loeb, Jacques.  Artificial Parthenogenesis and Fertilization.  Chicago, 1913.

2.  Loeb, Jacques.  The Organism as a Whole.  N.Y., 1916, p. 125—­brief summary of results of [1].

3.  Bower, Kerr & Agar.  Sex and Heredity.  N.Y., 1919, 119 pp.

4.  Schaefer, E.A.  Nature, Origin and Maintenance of Life.  Science, n.s., Vol. 36, pp. 306 f., 1912.

5.  Guyer, M.F.  Being Well-Born.  Indianapolis, 1916; p. 123.

CHAPTER II

SEX IN TERMS OF INTERNAL SECRETIONS

Continuity of germplasm; 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 egg and sperm in heredity; 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 man.

In Chapter I, the “immortality” of the protoplasm in the germ cells of higher animals, as well as in simpler forms without distinct bodies, was mentioned.  In these higher animals this protoplasm is known as germplasm, that in body cells as somatoplasm.

All that is really meant by “immortality” in a germplasm is continuity.  That is, while an individual may consist of a colony of millions of cells, all of these spring from one cell and it a germ cell—­the fertilized ovum.  This first divides to form a new group of germ cells, which are within the embryo or new body when it begins to develop, and so on through indefinite generations.  Thus the germ cells in an individual living to-day are the lineal descendants, by simple division, of the germ cells in his ancestors as many generations, or thousands of generations, ago as we care to imagine.  All the complicated body specializations and sex phenomena may be regarded as super-imposed upon or grouped around this succession of germ cells, continuous by simple division.

The type of body in each generation depends upon this germplasm, but the germplasm is not supposed to be in any way modified by the body (except, of course, that severe enough accidents might damage it).  Thus we resemble our parents only because the germplasm which directs our development is a split-off portion of the same continuous line of germ cells which directed their development, that of their fathers, and so on back.  This now universally accepted theory is called the “continuity of the germplasm.”