D E V E L O P M E N T S IN SEXUAL O R G A N O G E N E S I S
279
previously acquired by action of estradiol (Chang and Witschi, 1955). In
the first cross ( 9 ZW X neofemale ZW), the sex ratio among the offspring
indicates that WW females were obtained. These then have been tested
(Mikamo and Witschi, 1964) by the same grafting method. Females (WW)
have been changed to neomales (WW). These WW neomales, crossed with
normal ZW females, produced offspring that were all female (ZW and WW).
Contrary to the statements of Weiler and Ohno (1962), the analysis of
the karyotype of X. laevis done by Mikamo and Witschi (1966) does not
confirm the existence of a difference between the W and Z chromosomes.
Their observations had the advantage of being made on individuals of
ZZ, ZW, and WW constitution. Of the 36 chromosomes of the species, 11
are submetacentric and 7 subacrocentric. Testicular or ovarian development may result from each of the three types of genetic constitution.
As a whole these experiments, which take up again in a slightly different
form those of Humphrey (1945, 1948) on the axolotl, give evidence of
androgenic activity of the young differentiated testes and of the effect of
the male hormone on the sexual differentiation of the ovarian primordium.
2. Parabiosis in Anurans
The parabioses done in Rana and Hyla (Witschi, 1931) had shown that
the gonads of the male partner had a dominating effect and inhibited the
development of the ovaries, which finally became intersexual. Huchon
(1966) extended these experiments to Discoglossus pictus and Bombina
variegata. In Discoglossus, intersexuality is seen in the heterosexual pairs,
the male usually having a dominant effect on the female, which develops
ovotestes. Sometimes the effect of the intersexuality is reciprocal; in Bombina, no effect is observed in heterosexual combinations: the male and the
female possess testes and ovaries, respectively. In a general way, the
intersexual reaction in anurans, stimulated by the effect of male gonads on
ovarian differentiation, is much less marked than in urodeles. It may be
absent.
3. Relationship between Genetic Constitution and Sexual Differentiation
in Parabiosis
In the first parabiosis experiments on urodeles the two partners were
diploid individuals. In this case, for homospecific heterosexual pairs, it is
the male twin, in a general manner, although in varying degrees according
to the species, that has a dominant action, inducing involution of the
gonad, intersexuality, and in some cases sex reversal in the female.
The following combinations have been made in the triton, Pleurodeles
waltlii (Gallien and Beetschen, 1960; Gallien, 1963):
Diploid embryo (2n)-haploid embryo (ri)
Diploid embryo (2n)-triploid embryo (3n)
279
previously acquired by action of estradiol (Chang and Witschi, 1955). In
the first cross ( 9 ZW X neofemale ZW), the sex ratio among the offspring
indicates that WW females were obtained. These then have been tested
(Mikamo and Witschi, 1964) by the same grafting method. Females (WW)
have been changed to neomales (WW). These WW neomales, crossed with
normal ZW females, produced offspring that were all female (ZW and WW).
Contrary to the statements of Weiler and Ohno (1962), the analysis of
the karyotype of X. laevis done by Mikamo and Witschi (1966) does not
confirm the existence of a difference between the W and Z chromosomes.
Their observations had the advantage of being made on individuals of
ZZ, ZW, and WW constitution. Of the 36 chromosomes of the species, 11
are submetacentric and 7 subacrocentric. Testicular or ovarian development may result from each of the three types of genetic constitution.
As a whole these experiments, which take up again in a slightly different
form those of Humphrey (1945, 1948) on the axolotl, give evidence of
androgenic activity of the young differentiated testes and of the effect of
the male hormone on the sexual differentiation of the ovarian primordium.
2. Parabiosis in Anurans
The parabioses done in Rana and Hyla (Witschi, 1931) had shown that
the gonads of the male partner had a dominating effect and inhibited the
development of the ovaries, which finally became intersexual. Huchon
(1966) extended these experiments to Discoglossus pictus and Bombina
variegata. In Discoglossus, intersexuality is seen in the heterosexual pairs,
the male usually having a dominant effect on the female, which develops
ovotestes. Sometimes the effect of the intersexuality is reciprocal; in Bombina, no effect is observed in heterosexual combinations: the male and the
female possess testes and ovaries, respectively. In a general way, the
intersexual reaction in anurans, stimulated by the effect of male gonads on
ovarian differentiation, is much less marked than in urodeles. It may be
absent.
3. Relationship between Genetic Constitution and Sexual Differentiation
in Parabiosis
In the first parabiosis experiments on urodeles the two partners were
diploid individuals. In this case, for homospecific heterosexual pairs, it is
the male twin, in a general manner, although in varying degrees according
to the species, that has a dominant action, inducing involution of the
gonad, intersexuality, and in some cases sex reversal in the female.
The following combinations have been made in the triton, Pleurodeles
waltlii (Gallien and Beetschen, 1960; Gallien, 1963):
Diploid embryo (2n)-haploid embryo (ri)
Diploid embryo (2n)-triploid embryo (3n)