The sexual life of woman in its physiological, pathological and hygienic aspects

by E. Heinrich Kisch

7. Owing to the operation of these unknown influences, prediction of the sex of the offspring, and voluntary determination of the sex of the offspring, remain impossible. All we can say is that there is some probability that young and well-nourished mothers will procreate a comparatively larger number of female offspring, whilst elderly and ill-nourished mothers will procreate a comparatively larger number of male offspring.

II. Anatomical Investigations.

Of anatomical investigations and discoveries, those more especially relating to the sex-relationships of twins and triplets have been applied to the elucidation of the problem of the determination of sex.

The first and most important fact in this connection, one that is not merely a rule confirmed again and again by anatomists and gynecologists, but is further, as Mayrhofer has demonstrated as a result of his researches in von Braun’s clinic, a “natural law,” is this, that twins and triplets enclosed in a common chorion are invariably of the same sex. The sex-identity of such twins has been referred to the similarity of their nutritive conditions (Leuckart, Ploss), and more especially to the communication between their bloodvessels; and an intimate connection between these relationships and the determination of sex has been believed to exist.

Mayrhofer, however, opposes this assumption by the following deductions (“The Determination of Sex in the Human Species”); “Fœtuses enclosed within a single chorion always possess a common placenta, in which the blood-channels from both umbilical cords frequently, in the case of twins perhaps invariably, communicate. It might therefore be supposed that the sex-identity of embryos enclosed within a single chorion is due to the intermixture of their blood in the placenta. Hyrtl, however, describes a triplet’s placenta, in which, though all three fœtuses were enclosed within a single chorion, the vessels passing to the umbilical cord of one of the fœtuses were entirely distinct from the vascular area common to the two other fœtuses; it is therefore probable that in the case also of twins enclosed within a single chorion there is not necessarily any communication between their bloodvessels in the common placenta. But even if it were proved that in the case of twins enclosed within a single chorion their bloodvessels always do communicate in the common placenta, we could not therefore infer that the intermixture of the blood of the two fœtuses is the cause of their sexual identity.

“For the intermixture of the blood of the two fœtuses in the common placenta could never lead to a complete identity in the composition of the blood of the two; it could only lead to a diminution of the differences which would exist between the bloods if their placental circulations were entirely distinct, and the similarity in the bloods thus established could not be expected to do more than make it a general rule that such twins or triplets should be of the same sex; but to this rule exceptions might be expected to occur in certain cases, as when hæmatopoiesis in the two (or three) fœtuses was very different, or when the circulation through the intercommunicating bloodvessels was interfered with through the pressure of fibrinous deposits—differences between the bloods would then arise sufficient to cause differences in sex (if identical composition of the bloods is presumed to be the cause of the sexual identity).

“Experience teaches us that the existence of communicating vessels in the placenta does not suffice to induce a close similarity of growth and of the formation of the organs in twin fœtuses; nor does it prevent the illness and death of one fœtus leaving the health of the other undisturbed, although the communicating channels remain open; so that, if we except acardiac monsters, it is correct to say that each fœtus pursues a secluded life, uninfluenced by the life of its neighbour. Acardiac monsters, on the other hand, always receive blood which has already served for the nutrition of the normal fœtus, and the result of this is an arrested development and a striking preponderance of connective tissue in the acardiac twin. But notwithstanding the fact that the failure of its own proper circulation (which is indeed rendered possible by the existence of the communicating vessels in the placenta) leads to its defective nutrition with a blood inferior to that supplied to the normal fœtus, the acardiac monster is always of the same sex as the normal twin.”

From these considerations Mayrhofer rightly infers that the identity of sex of two fœtuses contained in a single chorion, since it does not depend upon the existence of communicating vessels in the placenta, must arise from a developmental tendency already existing in the two germs at the time of conception—or, in other words, that at the time of conception their sex is already inalterably determined.

This conclusion with respect to the sex of twins contained in a single chorion may very readily be extended to the inference that in the case of all human fœtuses the sex is already determined at the time of conception.

Another anatomical fact is that many twins are contained in a single chorion for this reason, that they originate from two germinal vesicles within a single ovum. It is an open question whether it is not possible for two embryos contained in separate chorions to come to lie in a single chorion through atrophy of the intermediate wall. If this is indeed possible, the invariable identity of sex in the case of fœtuses lying in a single chorion must lead us to agree with Mayrhofer in inferring that two ova lying within a single follicle, simultaneously fertilized, give rise to embryos of identical sex.