Part 63

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.

B. S. Schultze and Ahlfeld, as a result of the investigations regarding twins, also came to the conclusion that the sexual identity of twins depends upon their derivation from a single ovum. If, in accordance with what has been said above, an explanation of the sexual identity of certain twins is to be found in the fact that for such twins there has been a single conception only, and hence the influence, whatever it may be, by which sex is determined acts on both germs at the same time—still the sexual identity of twins in general is remarkable and has not yet been fully explained. The sexual identity in fact occurs much more frequently than appears to correspond to the percentage of twins derived from a single ovum. Von Fricks examined the data relating to multiple births in Prussia during the period of 1826 to 1879 and compiled the following table:

══════════════╤═════════════╤═════════════╤═════════════╤═════════════ Per Cent. │ Twins. │ Triplets. │Quadruplets. │Quintuplets. ──────────────┼─────────────┼─────────────┼─────────────┼───────────── Boys only │ 32.6│ 24.5│ 14.3│ 33.3 Girls only │ 30.3│ 22.5│ 19.4│ Boys and girls│ 37.1│ 53.0│ 66.3│ 66.7 ──────────────┼─────────────┼─────────────┼─────────────┼───────────── │ 2 B. 1 G. │ 28.5│ │ │ 1 B. 2 G. │ 24.5│ │ ──────────────┼─────────────┼─────────────┼─────────────┼───────────── │ │ 2 B. 2 G. │ 23.4│ │ │ 3 B. 1 G. │ 19.5│ │ │ 1 B. 3 G. │ 23.4│ ──────────────┼─────────────┼─────────────┼─────────────┼───────────── │ │ │ 4 B. 1 G. │ 33.3 │ │ │ 3 B. 2 G. │ 33.3 ══════════════╧═════════════╧═════════════╧═════════════╧═════════════

According to Ahlfeld, of twin births in general, the ratio of those with a common chorion to those with separate chorions is 1 : 8.15. If, however, we wished to explain the frequency with which twins are of identical sex from the occurrence of such twins derived from a single ovum, we should expect to find a very different ratio, namely, 1 : 3.84; that is to say, twins with a common chorion would have to be nearly three times as common as they actually are. From these facts Düsing endeavours to draw the conclusion that external conditions have an influence upon the determination of sex, for very many external conditions are identical in the case of twins; as, for instance, the age of the father, the age of the mother, the nutritive conditions of the ova and of the spermatozoa, the nutrition of the embryo, etc.—all of these would influence both the twins in the same direction. A difference in the sex of twins, on the other hand, might be due to two successive fertilizations.

B. S. Schultze has been led by his embryological studies to the conclusion that there are male and female ova. Thus he believes that sexually identical twins originate from a single ovum with two germinal vesicles, thus assuming that a double fertilization of such ova is possible. But since in such cases the sexes of the resulting twins are always identical the spermatozoon can have no influence upon the determination of sex, but the conditions leading to the development of one sex or the other must pre-exist in the ovum—i. e., there must be male and female ova.

That as a matter of actual fact in some cases the female progenitor exercises an overwhelming influence on the determination of sex, and that the opinion held by so many that this determination depends upon the mother alone is sometimes supported by facts, is shown by the incident recorded by Darwin (“Descent of Man,” Vol. I.), that an Arab mare was delivered seven times successively of a filly, never of a colt, although she was covered by seven different stallions. On the other hand, the circumstance, if it is not to be attributed to pure chance, can also be explained by the constitutional vigour of this mare (Hensen) without adopting the above hypothesis.

Recently Upjohn has maintained that there are two kinds of spermatozoa, male and female; the latter are the commonest, but the former are the more energetic.

An interesting anatomical fact bearing upon this question has been discovered by M. Nussbaum, namely, that in ascaris megalocephala the reproductive glands are indicated already before the separation of the germinal layers; and Nussbaum suggests that this is also the case in all animals, although the proof cannot be obtained in every instance.

Semper has shown also in the case of some of the plagiostomata that long before the beginning of the definitive development of the reproductive organs, the apparently hermaphrodite embryo already possesses at least the tendency toward the constitution of one sex or the other. For in these animals, at a time so early that as yet the reproductive glands exhibit no sexual differentiation whatever, the sexes can nevertheless be distinguished by what appears to be a secondary sexual character. In the female, namely, one ovary only is developed; and very early indeed in the embryos destined to become females we can observe an asymmetrical development of the two germinal furrows. By this characteristic the two sexes can be distinguished far earlier than it is possible to do so by the recognition of a histological differentiation of the reproductive glands.

According to Mayrhofer the prepotency of the male gives rise to the procreation of an excess of males in this way, that physical prosperity of the male probably leads to the generation of boys, whereas prosperity of the female tends to give rise to the generation of girls. Moreover, economizing of the semen by infrequent sexual intercourse tends to originate offspring of the male sex. In this connection Hensen remarks, apropos of the greater excess of male offspring among the Jews: “We might ask whether, in consequence of the comparative sexual continence of the Jews which demands a definite power of endurance on the part of the ova, there may not be effected a certain selection of the ova; and thus we may perhaps explain how it is that in this race an exceptional vigour is somewhat more often to be observed than in other races.” Bock assumes that “thinner semen,” such as results from more frequent sexual intercourse, favours the procreation of the female sex, whereas when intercourse is less frequent a larger number of boys is likely to be born. Janke indicates as two important fundamental principles of scientific physiology that, (1) sexual intercourse represents as it were a contest between the two parties to the sexual act as to which shall transmit his or her sexual influence to the child, the victor in the contest determining the sex of the offspring, and (2) that a crossed inheritance occurs, inasmuch as whichever progenitor proves stronger in this contest transmits to the child the sex other than his or her own. He therefore advises women who long to have a boy to drink a glass of champagne before fulfilling their conjugal duties in order to gain increased sexual vigour.

Fiquet also expresses the opinion that when a vigorous, passionate, and sanguine male progenitor has intercourse with a frigid and phlegmatic woman there will be a preponderant tendency for the offspring to be female; whereas, when the conditions are the opposite of these, the male progenitor being phlegmatic and cold, the female on the contrary sanguine, passionate, and ardent, the offspring will probably be of the male sex.

In opposition to these opinions of Fiquet and Janke, to the effect that the temperament and the sexual vigour of the progenitors have a determining influence in the origination of the sex of the offspring, Düsing insists that the quality of the reproductive products are alone influential. Düsing lays down the following proposition: “The greater the scarcity of individuals of one sex is, the more extensive consequently the demands made upon the sexual capacities of the individuals of that sex, the more rapidly their reproductive products are employed; and the younger these products therefore are when employed the more individuals of their own sex will appear among the offspring.”

Richarz believes, on the contrary, that the prepotency of the male gives rise to the procreation of more girls; a mother of high reproductive capacity will have more boys, one of less reproductive capacity, on the other hand, more girls.

Starkweather (“The Law of Sex,” London, 1883) states his view in the proposition: “The superior parent produces the opposite sex;” and he holds the quaint view that this superiority is displayed in certain anatomical characters of the face of the progenitor. He endeavours from the shape of the head and from the facial expression to deduce the superiority of the male and the female progenitor respectively. A high, square forehead, with prominent supra-ciliary ridges, constitutes, according to Starkweather, one of the principal symptoms of this superiority; important also are a strongly developed middle third to the nose, narrow lips, etc. He declares that in families known to him the possession of this Roman nose in the father is signalized by the possession also of a large number of daughters, while a Roman-nosed mother has many sons. The more the parents’ noses resemble each other the more equal will be the distribution of the sexes among the offspring. He connects this fact (!) also with the fact that the possessor of the aquiline nose is the ruler of the family. Men of great strength of character procreate chiefly daughters; women, on the other hand, with a powerful character and a firm will bring into the world a notable excess of boys. In the Southern States of the American union Starkweather found confirmation of his theory, since he observed there that among the offspring of white fathers and coloured mothers there was an excess of girls amounting to 12 to 15 per cent. Among the half-castes of Java, the so-called Lipplapps, in the third generation girls only are born, and these are sterile. The excess of girls in these cases depends upon the superiority of the white father; this superiority is transmitted to the few sons of the second generation, and these therefore procreate girls only to constitute the third generation; the latter are not powerful enough to bear children at all.

Roth has revived the old view that one ovary provides the germs for the male offspring, the other those for the female offspring. He believes further that in the process of cohabitation the mechanical impressions and stimuli received by one-half of the external genital organs, reinforced by contact with and pulling on the pubic hair, are transmitted through the pudic nerve and the hypogastric plexus to the corresponding half of the vagina and the uterus, to the Fallopian tube of that side and to the corresponding ovary. If, now, we can consider it as established (?), that in the human female one ovary discharges male ova only and the other female ova only, it seems to him that it is the corresponding half of the external genital organs, when specifically stimulated in sexual intercourse, and the consequently increased vital activity in the pudic nerve and its connections with the hypogastric plexus, that must be regarded as the organ by means of which sex is determined. Roth has also been informed by laymen that when for some time they have procreated daughters only they subsequently procreated sons, “when, having been accustomed to sleep on one side of their wife, they adopted the practice of sleeping on the other.”

Ricardi reports that in Modena the peasants say that a man whose wife has hitherto had daughters only, must, if he wishes to have a son, assume some other posture than usual in the performance of coitus.

III. Experimental Investigations.

A considerable number of years ago, Thury attacked the problem of the determination of sex by the experimental method. In his series of experiments he ascertained, using 29 cows, that in the case of 22 of these, which were served early in their heat, the calves were without exception heifers, while in the case of the remaining 7, which were served late in their heat, the calves were equally without exception bull-calves (Thury, “The Law of the Determination of the Sexes,” Leipzig, 1863); in the record of these experiments no mention is made of the age of the cows. Thury concluded that the sex was determined according to the fertilization of the ovum soon or late after its liberation from the ovary; namely, that an ovum fertilized soon after its discharge produced a female, whilst an ovum which had become comparatively old before it was fertilized became a male.

Thury’s sensational experiments gave rise to a succession of similar experiments, made mostly by cattle-breeders, above all in agricultural colleges and in stud-farms.

Some of these experiments were made in the agricultural colleges at Proskau and Eldera. The cows, which according to Thury’s views should have been delivered of heifers, were served as soon as their heat was observed (the heat lasted as a rule from 24 to 30 hours); these were delivered of 5 heifers and 5 bull-calves (in Proskau) and of 3 heifers and 5 bull-calves (in Eldera); the sexual ratio in these cases was therefore normal. On the other hand, cows which were not served until their heat had lasted for 20 hours were delivered (in Proskau) of 1 heifer and 4 bull-calves.

Further experiments (in Waldau) gave the result that cows served early were delivered of 1 heifer and 1 bull-calf. In another series (in Eldera) 9 cows served as soon as heat was observed (or, speaking strictly, in from ½ to 1½ hours of this), gave birth to 7 heifers and 2 bull-calves.

Experiments made at the Royal Friedrich Wilhelm Stud-Farm gave the following results: In the case of 20 mares, which if Thury’s theory had been correct should all have given birth to fillies, 11 only fulfilled this expectation; but 10, on the other hand, were colts. Touchon, in his experiments at Hohenhau, obtained 11 calves and 2 foals, exhibiting the sex expected in accordance with Thury’s theory.

Düsing made a compilation of the figures given in all the experiments made to test Thury’s theory, with the following results: Cows fertilized early were delivered of 13 bull-calves and 29 heifers; mares fertilized early were delivered of 10 colts and 13 fillies; cows fertilized late were delivered of 5 bull-calves and 2 heifers.

Gerbe made experiments on rabbits, putting the buck to some doe-rabbits soon after the beginning of their heat, but to others as late as possible in their heat. On examining the young in the horns of the uterus, from the ovary downward, the distribution of the sexes was found to be approximately equal.

Whilst Coste’s experiments on a hen gave results contradictory to Thury’s theory, Albini’s experiments, made also on the common fowl, gave results in agreement with that theory. He found that the hens began again to lay fertilized eggs 3 to 6 days after intercourse with the cock (from which they had previously been kept separate); on the average, the distribution of the sexes in the chickens hatched from these eggs was approximately equal, with, however, a slight preponderance of cock birds. On the ninth and tenth days after separation from the cock the eggs laid were half fertilized and half unfertilized; on the twelfth day after separation from the cock the unfertilized eggs were in a great majority; but even as late as the eighteenth day after separation some of the eggs laid were still fertilized. The fertilized eggs laid from the tenth to the fifteenth day after separation when incubated produced a great preponderance of hen birds.

We have to thank breeders for a large number of experiments, such as those made by the breeder Fiquet, at Houston in Texas, who found that a bull upon whose sexual capacities excessive demands were made, procreated bull-calves exclusively; whereas in herds containing numerous bulls there were found among the calves born a preponderance of heifers. In thirty experiments on cattle Fiquet always found that the larger the number of cows a bull had to serve, and the longer they were kept in service, the larger was the proportion of bull-calves among their offspring. On the other hand, if certain cows had their sexual desires first satisfied by a gelded animal and were then served by a vigorous and lusty bull, an excessive proportion of heifers was born to these animals.

Janke obtained similar results in the breeding of sheep. In a report made to Düsing he states that in the early part of the lambing season more ewe-lambs are born than rams; in the latter part of the lambing season, on the contrary, more rams than ewes. The explanation he gives is that at the commencement of the pairing the rams are fresh and lusty, whilst later their potency is comparatively exhausted. In stud-farms, according to the same observer, it is a familiar experience that the most vigorous stallions serving a mare in the morning commonly procreate a filly; but if later in the day they serve a second mare they almost always procreate a colt. This, he thinks, finds its explanation in the fact that the stallion, when he serves the second mare, is in a condition of comparative sexual exhaustion, the more so because he usually covers the first mare twice.