234
WILLIAM C. YOUNG
by Gallien (28) that a relationship exists between the nature of the
homogametic sex and that of the hormone producing sex reversal, and
from the experience with domestic fowl (page 235), the last possibility would be predicted.
Important experiments have been performed on amphibian larvae
and adults. Within this phylum, the possibility that androgenic and
estrogenic substances have an organizing action seems likely, but as
with the work on fishes critical tests have not been made. Equally important, the complexities of tissue responsiveness (381, 407) may apply
to behavior as well; consequently caution in interpretation is indicated.
An early attempt to reverse the sex in a species that would breed in the
laboratory was rewarded when Humphrey (25) raised sex-reversed
female Mexican axolotls in which testis preprimordia had been implanted
into female larvae. The mating activity of these animals was typically
masculine. Other investigators have obtained sex reversal by adding
androgenic or estrogenic substances to the aquarium water at about the
time the tadpoles begin eating. Genetic female Rana temporaria receiving testosterone propionate were transformed completely and permanently into individuals which functioned as males (408). The addition of estradiol benzoate to water containing the urodele Pleurodeles
waltlii and the anuran Xenopus hevis resulted in the feminization of
genetic males (26-28, 407, 409). In Xenopus hevis androgens interfere
little with the development of the ovaries of genetic females, but the
behavior is modified, and immediately after metamorphosis vigorous
clasping behavior is shown (29). When male Xenopus tadpoles were
exposed to estradiol benzoate, the entire animal was completely feminized. As was predicted, these sex-reversed males when bred with normal males produced only male offspring (SO). Noting that the estradiol
need be administered only during a short larval period, they added the
important generalization that in the process of oogenesis and development of the female secondary sex characters including behavior, the
genes play an active role only during a short and definite period. Beyond
this point presumably the hormones become effective agents (28, 407).
With respect to birds, the only data bearing on the relationship of
hormones administered during the embryonic period to the behavior
displayed after hatching have been obtained by investigators who have
used the domestic fowl. In most cases estrogens or androgens were
injected into the allantoic or amniotic cavity, usually within the first 4
days of the incubation period. More recently eggs have been dipped for
5-20 seconds into a variety of steroids and then replaced in the incubator until hatching (410). Except for the Pincus and Hopkins (410) study
in which the embryos were subjected to androgenic and estrogenic
WILLIAM C. YOUNG
by Gallien (28) that a relationship exists between the nature of the
homogametic sex and that of the hormone producing sex reversal, and
from the experience with domestic fowl (page 235), the last possibility would be predicted.
Important experiments have been performed on amphibian larvae
and adults. Within this phylum, the possibility that androgenic and
estrogenic substances have an organizing action seems likely, but as
with the work on fishes critical tests have not been made. Equally important, the complexities of tissue responsiveness (381, 407) may apply
to behavior as well; consequently caution in interpretation is indicated.
An early attempt to reverse the sex in a species that would breed in the
laboratory was rewarded when Humphrey (25) raised sex-reversed
female Mexican axolotls in which testis preprimordia had been implanted
into female larvae. The mating activity of these animals was typically
masculine. Other investigators have obtained sex reversal by adding
androgenic or estrogenic substances to the aquarium water at about the
time the tadpoles begin eating. Genetic female Rana temporaria receiving testosterone propionate were transformed completely and permanently into individuals which functioned as males (408). The addition of estradiol benzoate to water containing the urodele Pleurodeles
waltlii and the anuran Xenopus hevis resulted in the feminization of
genetic males (26-28, 407, 409). In Xenopus hevis androgens interfere
little with the development of the ovaries of genetic females, but the
behavior is modified, and immediately after metamorphosis vigorous
clasping behavior is shown (29). When male Xenopus tadpoles were
exposed to estradiol benzoate, the entire animal was completely feminized. As was predicted, these sex-reversed males when bred with normal males produced only male offspring (SO). Noting that the estradiol
need be administered only during a short larval period, they added the
important generalization that in the process of oogenesis and development of the female secondary sex characters including behavior, the
genes play an active role only during a short and definite period. Beyond
this point presumably the hormones become effective agents (28, 407).
With respect to birds, the only data bearing on the relationship of
hormones administered during the embryonic period to the behavior
displayed after hatching have been obtained by investigators who have
used the domestic fowl. In most cases estrogens or androgens were
injected into the allantoic or amniotic cavity, usually within the first 4
days of the incubation period. More recently eggs have been dipped for
5-20 seconds into a variety of steroids and then replaced in the incubator until hatching (410). Except for the Pincus and Hopkins (410) study
in which the embryos were subjected to androgenic and estrogenic