Abstract:
G.K. Noble has suggested that the spring migration of
amphibians to water prior to breeding ’’may be considered
a secondary sexual character found in both sexes'* (Noble,
# *
1933), p,402), and in addition he points out that the sex
0
hormones, which determine the appearance of the anatomical
secondary sexual characters, may also influence the
appearance of the seasonal movement to water* Blair (1946)
also considers that what he terms the "mating reaction*1 of
✓
Bufo fowleri. which consists of the spring migration to
0
water and the subsequent breeding activities, are under
hormonal control* He was, however, unable to elicit any
of these reactions by hormonal treatment. Other workers
have recorded that the clasp reflex can be induced in Bufo
by pituitary implants (e.g. Houssay, Guisti & Lascano-
Gongales, 1929), but there appears to be no report in the
literature of the induction of the complete sexual behaviour
in Bufo by the injection of the sex hormones. It seems that
0
in this respect Bufo is very peculiar, since a review of the
literature shows that it is characteristic of animals
studied from all the vertebrate olasoes that sexual behavior is as much a part of the reproductive equipment of the
animal as are the organs of reproduction, and, like these
organs, it falls under a marked and specific influence of
the sex hormones* Blair and Noble believe that there 0x0
also environmental factors which influence the seasonal
*
water drive and sexual behaviour, in addition to the hormonal
factors, and certainly while it is clear from the literature
that the environment, acting on the central nervous system,
is of critical importance in the appearance of sexual
behaviour, the level of the sex hoinones must also be a
critical factor in its appearance. The literature indeed
shows that sensory stimulation and the sex hormone level
(among other internal factors) appear to be complementary
elements in the evocation of sexual behaviour, and it is
therefore reasonable to look for the effects of the sex
hormones on the breeding behaviour of Bufo. in spite of the
largely negative results that have so far been obtained.
It is, moreover, evident from the literature that the
development of the cerebral cortex in the vertebrate series
seems to be inversely related to the indispensibility of
the sex hormones in the appearance of sexual behaviour*
Because of the relatively poor development of the anuran
brain, it is further to be expected that Bufo should show
any responses to sex hormone treatment that might exist in a particularly well marked manner. A review of the
literature does, 121 fact, show that there is ample
justification for further investigations into the effects
of the sex hormones on the general breeding behaviour of
✓
toads, and the following review will be concerned with the
two main considerations given above, namely that i) sensory
stimulation and the sex hormone level appear to exert a
finqi role in the evocation of sexual behaviour, and that
ii) the influence of the sex hormones on behaviour seems to
be Inversely related to the development of the cerebral
cortex.
