pigmented papillae is cast off, and the thumb remains comparatively smooth
from April or May until August or September. When the large papillae are
shed, smaller papillae remain beneath, and are gradually obliterated by
the epidermis growing up between them. The epidermis is therefore growing
while the spermatogenesis is taking place. In August and September the
epidermic papillae begin to be obvious, and from this time till February a
continuous increase in the papillae and their pigmentation occur. Geoffrey
Smith argues that the development of this somatic character occurs while
the testes are inactive and unchanged. Considering that the testes
throughout the winter months are crammed with spermatozoa, which must
require some nourishment, and which may be giving off a hormone all the
time, the argument has very little weight. Smith and Schuster found that
ovariotomy, with or without subsequent implantation of testes or injection
of testis extract, had no effect in causing the thumb of the female to
assume any male characters.

Castration during the breeding season causes the external pigmented
layer with its papillae to be cast off very soon--that is to say, it
has the same effect as the normal discharge of the spermatozoa. Smith
and Schuster found that castration at other seasons caused the pad to
remain in the condition in which it was at the time, that there was no
reduction or absorption as Nussbaum and Meisenheimer found, and that
allo-transplantation of testes--that is, the introduction of testes from
other frogs either into the dorsal lymph-sacs or into the abdominal
cavity--or the injection of testis extract, had no effect in causing
growth or development of the thumb-pad.

There seems to be one defect in the papers of both Nussbaum and Smith and
Schuster--namely, that neither of them mentions or apparently appreciates
the fact that the thumb-pads, apart from the dermal glands, consist of