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Updated: April 30, 2025
Spermatogenesis is not the only source of the testicular hormone: changes in the secretory activity of the interstitial cells or spermatocytes are sufficient to account for periodic development of somatic sex-characters, and the same reasoning applies to the antlers of stags. The milk glands in Mammals constitute one of the most remarkable of secondary sexual characters.
The males have sexual instincts, themselves dependent on the testicular hormone, which develop sexual jealousy and rivalry, and the Ruminants fight by butting with their heads because they have no incisor teeth in the upper jaw, or tusks, which are used in fighting in other species.
To suppose that a secretion could be so complicated in its action as to determine each one of a thousand different items of structure, colour and behaviour would be preposterous. We may say that it cannot possibly be that the ovarian or testicular secretion is composed of enough different chemical substances to produce each different effect.
In these as in other respects the ovaries are precisely analogous to the testes. They not only form the ova, but they elaborate for internal use a secretion which develops and maintains the special physical and mental qualities of womanhood, as the testicular secretion those of manhood.
Perhaps, as applied to the period below puberty, it would be more exact to say "pseudo-sexuality." Matsumato has lately pointed out the significance of the fact that the interstitial testicular tissue, essential to the hormonic function of the testes, only becomes active at puberty.
When the bird was killed some months after the operation, a greater or lesser amount of regenerated testicular tissue was found either on the original site of the organs or engrafted upon neighbouring organs. This experience, it will be noted, agrees with my own in the case of fowls.
Masculising of females was much more difficult than feminising of males because the testicular tissue was less resistent, and could not be grafted so easily. When it succeeded, however, degeneration of the seminal tubules took place, with increase of the interstitial or Leydig's cells. The vaginal opening in rats disappeared, partly or completely.
In one particular case only a minute nodule of testicular tissue showing normal spermatogenesis was found on post mortem examination attached to the intestine. In this bird there was no male development of comb or wattles, a full development of neck hackles, a certain development of saddle hackles, a few straggling badly curved feathers in the tail and short blunt spurs on the legs.
As the ovaries are strictly analogous to the testes, it was surmised that ovarian extract might prove a drug equally valuable with testicular products. As a matter of fact, ovarian extract, in the form of ovarin, etc., would seem to have proved beneficial in various disorders, more especially in anæmia and in troubles due to the artificial menopause.
We must then look upon the internal secretion as composed of the liquid elements of the testicular secretion. So far as physiologists know at present, the external secretion differs from the internal secretion only in possessing spermatozoa.
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