e Steinach compares to those noted in
the human species during childhood.[6]

The genesic tendencies are thus, to a certain degree, independent of the
generative glands, although the development of these glands serves to
increase the genesic ability and to furnish the impulsion necessary to
assure procreation, as well as to insure the development of the secondary
sexual characters, probably by the influence of secretions elaborated and
thrown into the system from the primary sexual glands.[7]

Halban ("Die Entstehung der Geschlechtscharaktere," _Archiv fuer
Gynaekologie_, 1903, pp. 205-308) argues that the primary sex
glands do not necessarily produce the secondary sex characters,
nor inhibit the development of those characteristic of the
opposite sex. It is indeed the rule, but it is not the inevitable
result. Sexual differences exist from the first. Nussbaum made
experiments on frogs (_Rana fusca_), which go through a yearly
cycle of secondary sexual changes at the period of heat. These
changes cease on castration, but, if the testes of other frogs
are introduced beneath the skin of the castrated frogs, Nussbaum
found that they acted as if the frog had not been castrated. It
is the secretion of the testes which produces the secondary
sexual changes. But Nussbaum found that the testicular secretion
does not work if the nerves of the secondary sexual region are
cut, and that the secretion has no direct action on the organism.
Pflueger, discussing these experiments (_Archiv fuer die Gesammte
Physiologie_, 1907, vol. cxvi, parts 5 and 6), disputes this
conclusion, and argues that the secretion is not dependent on the
action of the nervous system, and that therefore the secondary
sexual characters are independent of the nervous system.

Steinach has also in later experiments ("Geschlechtstrieb und
echt Sekundaere Geschlechtsmerkmale als Folge der
innerskretorischen Funktion der Keimdrusen," _Zentralblatt fuer
Physiologie_, Bd. xxiv, Nu. 13, 1910) argued against any local
nervous influence. He found in _Rana fusca_ and _esculenta_ that
after castration in autumn the impulse to grasp the female
persisted in some degrees and then disappeared, reappearing in a
slight degree, however, every winter at the normal period of
sexual activity. But when the testicular substance of actively
sexual frogs was injecte