Study of secondary sexual characters is bound up with consideration of the effect of internal secretions of the genital glands on general metabolism. The relation of this influence or its absence (as in the case of artificially castrated animals) has been traced out in the degree of development of the secondary characters. The internal secretions, however, undoubtedly have an influence on all the cells of the body. This is clearly shown by the changes which occur at puberty in all parts of the body, and not only in the seats of the secondary sexual characters. As a matter of fact, the internal secretions of all the glands must be regarded as affecting all the tissues. The internal secretions of the genital glands must be regarded as completing the sexuality of the individual. Every cell must be considered as possessing an original sexuality, to which the influence of the internal secretion in sufficient quantity is the final determining condition under the influence of which the cell acquires its final determinate character as male or female. The genital glands are the organs in which the sex of the individual is most obvious, and in the component cells of which it is most conspicuously visible. At the same time it must be noted that the distinguishing characters of the species, race and family to which an organism belongs are also best marked in the genital cells. Just as Steenstrup, on the one hand, was right in teaching that sex extends all over the body and is not confined to the genital organs, so, on the other hand, Naegeli, de Vries, Oskar Hertwig and others have propounded the important theory, and supported it by weighty arguments, that every cell in a multi-cellular organism possesses a combination of the characters of its species and race, but that these characters are, as it were, specially condensed in the sexual cells. Probably this view of the case will come to be accepted by all investigators, since every living being owes its origin to the cleavage and multiplication of a single cell.