theory. It can scarcely be said that they carry conviction. We
may rather agree with Guinard that so great is the importance of
reproduction that nature has multiplied the means by which
preparation is made for the conjunction of the sexes and the
roads by which sexual excitation may arrive. As Hirschfeld puts
it, in a discussion of this subject (_Sexual-Probleme_, Feb.,
1912), "Nature has several irons in the fire."

It will be seen that the conclusions we have reached indirectly
involve the assumption that the spinal nervous centers, through
which the sexual mechanism operates, are not sufficient to
account for the whole of the phenomena of the sexual impulse. The
nervous circuit tends to involve a cerebral element, which may
sometimes be of dominant importance. Various investigators, from
the time of Gall onward, have attempted to localize the sexual
instinct centrally. Such attempts, however, cannot be said to
have succeeded, although they tend to show that there is a real
connection between the brain and the generative organs. Thus
Ceni, of Modena, by experiments on chickens, claims to have
proved the influence of the cortical centers of procreation on
the faculty of generation, for he found that lesions of the
cortex led to sterility corresponding in degree to the lesion;
but as these results followed even independently of any
disturbance of the sexual instinct, their significance is not
altogether clear (Carlo Ceni, "L'Influenza dei Centri Corticali
sui Fenomeni della Generazione," _Revista Sperimentale di
Freniatria_, 1907, fasc. 2-3). At present, as Obici and
Marchesini have well remarked, all that we can do is to assume
the existence of cerebral as well as spinal sexual centers; a
cerebral sexual center, in the strictest sense, remains purely