DEVELOPMENTS IN SEXUAL ORGANOGENESIS
269
pupa. This is the stage at which the reproductive tract and somatic sexual
characteristics differentiate.
The interesting point is that, at the time of its differentiation, the testicular structure displays at its apex some mesodermal tissue called apical
tissue, which will act as an androgenic endocrine gland. The tissue is active
from the time of its differentiation. It functions between the third molt and
the pupal molt. After that it regresses and disappears. Extensive development of the apical tissue is characteristic of the lampyrids.
In the female the ovarian follicles, which differentiate after the third
molt, do not possess this apical tissue. It is represented initially by only a
few apical cells that rapidly undergo histolysis. In the ovarian follicles,
primordial germ cells and prefollicular cells multiply during the larval
stage. A short time before the pupal molt, the primordial germ cells develop
into oogonia, then, at the pupal stage, into oocytes. On the whole the
endocrine apical tissue, which will be shown to be androgenic, develops
only in the male. It is the characteristic feature of the condition that will
control sexual differentiation.
By a series of experiments, Naisse was able to supply definitive proof of
this. If one or two testes from larvae after the third, fourth, or fifth molt,
that is, in the last three larval stages, are implanted in the abdomen of
larval females between the third and sixth molts, the females are completely
masculinized. The ovaries of the host are transformed into functional
testes, the genital ducts of the adults obtained are of the male type, as are
the somatic sexual characteristics. These neomales behave as normal males.
They are competent to fertilize females.
If under the same conditions the testes are implanted in female pupae,
rather than before the pupal molt, these pupae develop into females. This
indicates that determination of ovaries occurs at this stage and that the
androgenic effect of the apical tissue can no longer modify the ovarian
region.
The activity of the apical tissue is terminated shortly before the pupal
molt. Testes removed at this age and implanted in larval females before the
pupal molt produce only rare instances of masculinization. Testes of pupae
or of adults, no matter what the age of the host into which they are grafted,
produce no masculinization.
Thus the pupal molt is a critical stage. Before that, the testis, owing to
its apical tissue, is masculinizing. After that, it is not active. This corresponds to the disappearance of the apical tissue. As for the ovary, it is
responsive and labile before the pupal stage. Its determination is acquired
at that time. These facts recall those known for vertebrates. If they are also
comparable, in essence, to the action demonstrated for the androgenic
gland of crustaceans, it should be noted that, in the latter case, the activity
of the androgenic gland and the ability of the gonads, even in the adult, to
269
pupa. This is the stage at which the reproductive tract and somatic sexual
characteristics differentiate.
The interesting point is that, at the time of its differentiation, the testicular structure displays at its apex some mesodermal tissue called apical
tissue, which will act as an androgenic endocrine gland. The tissue is active
from the time of its differentiation. It functions between the third molt and
the pupal molt. After that it regresses and disappears. Extensive development of the apical tissue is characteristic of the lampyrids.
In the female the ovarian follicles, which differentiate after the third
molt, do not possess this apical tissue. It is represented initially by only a
few apical cells that rapidly undergo histolysis. In the ovarian follicles,
primordial germ cells and prefollicular cells multiply during the larval
stage. A short time before the pupal molt, the primordial germ cells develop
into oogonia, then, at the pupal stage, into oocytes. On the whole the
endocrine apical tissue, which will be shown to be androgenic, develops
only in the male. It is the characteristic feature of the condition that will
control sexual differentiation.
By a series of experiments, Naisse was able to supply definitive proof of
this. If one or two testes from larvae after the third, fourth, or fifth molt,
that is, in the last three larval stages, are implanted in the abdomen of
larval females between the third and sixth molts, the females are completely
masculinized. The ovaries of the host are transformed into functional
testes, the genital ducts of the adults obtained are of the male type, as are
the somatic sexual characteristics. These neomales behave as normal males.
They are competent to fertilize females.
If under the same conditions the testes are implanted in female pupae,
rather than before the pupal molt, these pupae develop into females. This
indicates that determination of ovaries occurs at this stage and that the
androgenic effect of the apical tissue can no longer modify the ovarian
region.
The activity of the apical tissue is terminated shortly before the pupal
molt. Testes removed at this age and implanted in larval females before the
pupal molt produce only rare instances of masculinization. Testes of pupae
or of adults, no matter what the age of the host into which they are grafted,
produce no masculinization.
Thus the pupal molt is a critical stage. Before that, the testis, owing to
its apical tissue, is masculinizing. After that, it is not active. This corresponds to the disappearance of the apical tissue. As for the ovary, it is
responsive and labile before the pupal stage. Its determination is acquired
at that time. These facts recall those known for vertebrates. If they are also
comparable, in essence, to the action demonstrated for the androgenic
gland of crustaceans, it should be noted that, in the latter case, the activity
of the androgenic gland and the ability of the gonads, even in the adult, to