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.
Many phenomena, amongst which may be noticed specially experiments on the regeneration of lost parts and investigations into the chemical differences between the corresponding tissues of nearly allied animals, have led the investigators to whom I have just referred to conceive the existence of an “Idioplasm,” which is the bearer of the specific characters, and which exists in all the cells of a multi-cellular animal, quite apart from the purposes of reproduction. In a similar fashion I have been led to the conception of an “Arrhenoplasm” (male plasm) and a “Thelyplasm” (female plasm) as the two modes in which the idioplasm of every bisexual organism may appear, and which are to be considered, because of reasons which I shall explain, as ideal conditions between which the actual conditions always lie. Actually existing protoplasm is to be thought of as moving from an ideal arrhenoplasm through a real or imaginary indifferent condition (true hermaphroditism) towards a protoplasm that approaches, but never actually reaches, an ideal thelyplasm. This conception brings to a point what I have been trying to say. I apologise for the new terms, but they are more than devices to call attention to a new idea.