304
L. G A L L I E N
must surely be a question of two sexually different genotypes (9 /& ). The
male co-twin thus would have been able to exert a dominating effect on
sexual differentiation. It is known that in the mouse, as in other mammals,
testicular differentiation begins before that of the ovaries, with the result
that the testicular tissue of the male would be able to have an effect on the
differentiation of the composite gonads at a very early stage. However, the
fact that intersexes were obtained indicates that further research is needed
before this can be considered as a general explanation. Each of the three
intersexes has a different kind of structure of the gonad : ovary-ovotestis,
ovotestis-ovotestis, and ovary-testis. The nature of the genital ducts
depends on the kind of gonad that is adjacent to them. Ovotestes result in
the persistance of Wolffian and Mullerian ducts, but only one of these is
well developed.
Tarkowski compares his observations with known cases of true hermaphroditism that appear spontaneously. In a case analysed by Gartler
et al. (1962), a child possessed a left ovary of XX genetic type, and on
the right an ovotestis with a mixture of XX and XY cells, the latter being
predominant. It is possible, according to Tarkowski, that the mouse
chimerae studied correspond to such an X X / X Y type. However, the genetic
sex of the germ cells of the hermaphroditic chimerae remains unknown. It
is not impossible that the occurrence together of oocytes and male germ
cells reflects only the secondary differentiation of the germ cells, without
necessarily indicating their genetic sex. In this regard it is appropriate to
recall that oocytes and spermatogonia can coexist, at least for a time, in
testicular tissue, whether it be following a testicular graft (cf. Ponse, 1949)
or in an intersexual gonad (Gallien, 1954, 1956).
Whatever causative mechanisms may be involved in Tarkowski's experiments, the method of fusion of two blastomeres permits an attack on
certain aspects of intersexuality in mammals and the conflicts between
the effects of genetic constitution and epigenetic factors.
Finally, the mosaic constitution of mouse blastocysts resulting from a
very early union of two eggs has also been accomplished by Mintz (1964).
In a very significant series of experiments, she has fused eggs from a viable
line with those from a lethal mutant, tailless (t
12
/l
12 ). The characteristics
of the blastomeres of the mutant make it possible to identify them. These
studies are closely related to those of Tarkowski.
4. Perspectives in the Analysis of the Freemartin Effect
In relation to the preceding facts, it is appropriate to point out certain
recent observations that open up new prospects for analysis of the freemartin in cattle (Bos taurus).
The hormonal theory proposed by Lillie (1916, 1917) to account for the
freemartin effect remains the most reasonable explanation.
L. G A L L I E N
must surely be a question of two sexually different genotypes (9 /& ). The
male co-twin thus would have been able to exert a dominating effect on
sexual differentiation. It is known that in the mouse, as in other mammals,
testicular differentiation begins before that of the ovaries, with the result
that the testicular tissue of the male would be able to have an effect on the
differentiation of the composite gonads at a very early stage. However, the
fact that intersexes were obtained indicates that further research is needed
before this can be considered as a general explanation. Each of the three
intersexes has a different kind of structure of the gonad : ovary-ovotestis,
ovotestis-ovotestis, and ovary-testis. The nature of the genital ducts
depends on the kind of gonad that is adjacent to them. Ovotestes result in
the persistance of Wolffian and Mullerian ducts, but only one of these is
well developed.
Tarkowski compares his observations with known cases of true hermaphroditism that appear spontaneously. In a case analysed by Gartler
et al. (1962), a child possessed a left ovary of XX genetic type, and on
the right an ovotestis with a mixture of XX and XY cells, the latter being
predominant. It is possible, according to Tarkowski, that the mouse
chimerae studied correspond to such an X X / X Y type. However, the genetic
sex of the germ cells of the hermaphroditic chimerae remains unknown. It
is not impossible that the occurrence together of oocytes and male germ
cells reflects only the secondary differentiation of the germ cells, without
necessarily indicating their genetic sex. In this regard it is appropriate to
recall that oocytes and spermatogonia can coexist, at least for a time, in
testicular tissue, whether it be following a testicular graft (cf. Ponse, 1949)
or in an intersexual gonad (Gallien, 1954, 1956).
Whatever causative mechanisms may be involved in Tarkowski's experiments, the method of fusion of two blastomeres permits an attack on
certain aspects of intersexuality in mammals and the conflicts between
the effects of genetic constitution and epigenetic factors.
Finally, the mosaic constitution of mouse blastocysts resulting from a
very early union of two eggs has also been accomplished by Mintz (1964).
In a very significant series of experiments, she has fused eggs from a viable
line with those from a lethal mutant, tailless (t
12
/l
12 ). The characteristics
of the blastomeres of the mutant make it possible to identify them. These
studies are closely related to those of Tarkowski.
4. Perspectives in the Analysis of the Freemartin Effect
In relation to the preceding facts, it is appropriate to point out certain
recent observations that open up new prospects for analysis of the freemartin in cattle (Bos taurus).
The hormonal theory proposed by Lillie (1916, 1917) to account for the
freemartin effect remains the most reasonable explanation.