D E V E L O P M E N T S I N SEXUAL O R G A N O G E N E S I S
295
the gonad as gynogenic and androgenic inductor regions respectively. (5)
Animals with a female genetic constitution (ZW, WW, or XX) can undergo
spermatogenesis just as genetic males (ZZ, XY, or YY) can undergo
oogenesis. (6) Organisms with WW and YY genetic constitution, which
normally do not exist, can be obtained. (7) Eggs with a ZZ constitution
and lacking a W chromosome can differentiate into females, just as WW
eggs can develop into males. This demonstrates that the influence of sexual
factors associated with hétérochromosomes is not necessarily decisive for
the differentiation of sex. Consequently, genes of sexuality of a type opposed to those of the hétérochromosomes must be present in the autosomes.
2. Permanence of Genetic Control: Return to the Genetic Sex after the
Change in Direction of Sexual Organogenesis
Analysis of the actions of hormones in the differentiation of sex of the
gonads in amphibians indicates clearly that two phenomena may interfere
in the course of sexual organogenesis: hereditary sexual constitution and
hormonal control. In the case of exogenous steroid hormones administered
during development, it appears that they are able to override the normal
genetic control. But this dominance is most often partial, and the intersexual individuals tend to return to a differentiation of the gonads that
conforms to the genetic sex. These facts have been clearly demonstrated in
amphibians and birds.
a. Amphibians. Even in species such as Pleurodeles that can undergo
complete reversal in a d
71
—> 9 direction, if the initial reversal is not absolutely complete (strong intersexuality), or in other words, if any vestige
of medullary tissue remains, these animals finally resume development of
testicular tissue, while the important ovarian structures disappear completely (Fig. 17). It is only when all medullary vestiges have been
abolished that reversal is permanent. The strength of this ability to return
to the genetic sex is considerable. Thus a genetic male (ZZ) changed into
a functional female, with all offspring 100% males (ZZ), can, after several
years, develop a functional testis (Gallien, 1961, 1962b). In Pelobates and
Triturus, instability of sex reversal of the gonads after treatment with
estradiol has likewise been observed (Collenot, 1965).
b. Birds. In the embryo chick very strong intersexuality in the cf —> 9
direction after treatment with estrone can be obtained. However, this
subtotal reversal is not stable; the gonads, after the end of incubation, form
testes, even if the feminizing treatment is maintained at a high level (Wolff,
1936).
The analysis of this phenomenon has been approached by organ culture
methods and intracoelomic grafts (Wolff and Haffen, 1961; Haffen, 1964).
If, in a culture in vitro, a feminized male gonad (ZZ) is placed under the
same experimental conditions as a normal ovary (ZW), the cortex of the
295
the gonad as gynogenic and androgenic inductor regions respectively. (5)
Animals with a female genetic constitution (ZW, WW, or XX) can undergo
spermatogenesis just as genetic males (ZZ, XY, or YY) can undergo
oogenesis. (6) Organisms with WW and YY genetic constitution, which
normally do not exist, can be obtained. (7) Eggs with a ZZ constitution
and lacking a W chromosome can differentiate into females, just as WW
eggs can develop into males. This demonstrates that the influence of sexual
factors associated with hétérochromosomes is not necessarily decisive for
the differentiation of sex. Consequently, genes of sexuality of a type opposed to those of the hétérochromosomes must be present in the autosomes.
2. Permanence of Genetic Control: Return to the Genetic Sex after the
Change in Direction of Sexual Organogenesis
Analysis of the actions of hormones in the differentiation of sex of the
gonads in amphibians indicates clearly that two phenomena may interfere
in the course of sexual organogenesis: hereditary sexual constitution and
hormonal control. In the case of exogenous steroid hormones administered
during development, it appears that they are able to override the normal
genetic control. But this dominance is most often partial, and the intersexual individuals tend to return to a differentiation of the gonads that
conforms to the genetic sex. These facts have been clearly demonstrated in
amphibians and birds.
a. Amphibians. Even in species such as Pleurodeles that can undergo
complete reversal in a d
71
—> 9 direction, if the initial reversal is not absolutely complete (strong intersexuality), or in other words, if any vestige
of medullary tissue remains, these animals finally resume development of
testicular tissue, while the important ovarian structures disappear completely (Fig. 17). It is only when all medullary vestiges have been
abolished that reversal is permanent. The strength of this ability to return
to the genetic sex is considerable. Thus a genetic male (ZZ) changed into
a functional female, with all offspring 100% males (ZZ), can, after several
years, develop a functional testis (Gallien, 1961, 1962b). In Pelobates and
Triturus, instability of sex reversal of the gonads after treatment with
estradiol has likewise been observed (Collenot, 1965).
b. Birds. In the embryo chick very strong intersexuality in the cf —> 9
direction after treatment with estrone can be obtained. However, this
subtotal reversal is not stable; the gonads, after the end of incubation, form
testes, even if the feminizing treatment is maintained at a high level (Wolff,
1936).
The analysis of this phenomenon has been approached by organ culture
methods and intracoelomic grafts (Wolff and Haffen, 1961; Haffen, 1964).
If, in a culture in vitro, a feminized male gonad (ZZ) is placed under the
same experimental conditions as a normal ovary (ZW), the cortex of the