Part 16

“All nature is but art unknown to thee, All chance, direction which thou canst not see.”—POPE.

Hitherto no theory has been advanced which explained, in any satisfactory or credible manner, the conception of twins of opposite sex. I maintain, however, that, in the light of my investigations, it becomes a simple and natural occurrence, and in this chapter I will briefly outline the circumstances from which it may arise.

Twins may be conceived in two or three different ways:

1. A boy may have started at the beginning of the month, or toward the middle, and a girl may be conceived seven days later or more, just before the next period is due; the fact that the uterus does not always close up entirely, and may even slightly re-open after conception, has been sufficiently proved to make such an event entirely probable. To give an instance, an American biologist mentions the case of a white woman who gave birth to twins on two successive days, of which one was white and the other black. She subsequently admitted intercourse with a coloured man a few days after her husband had left her for a long period. Quite clearly this woman conceived each twin on a different day, by a different father.

The fact that so often, where the twins are of opposite sexes, one seems to be less developed than the other, points to the probability of one of them having been conceived one, two or three weeks later than the other. When the girl is the smaller, which is often the case, we may conclude she was the last conceived. If the boy be the smaller he was conceived perhaps at a later date, and after the attempt at menstruation which often occurs during the first or second month of girl-pregnancy. I believe this manner of twin-conception to be rare, however. Out of twelve cases of mixed twins collected recently, I have found only one where the boy was smaller.

2. A boy may be conceived simultaneously with a girl if the ova from both ovaries happen to be present in the tubes or uterus at the same time. This would occur in the “blank week,” which, as we explained previously, does not exist for certain women, if their period arrives every three weeks. So, at the end of fifteen days, from the first day of period, the left ovary, already active, his discharged an ovum before the male ovum discharged by the right ovary has fully lost its vitality. Where this is the case, both of these ova are equally ready for fertilisation. This manner of conception is probably much rarer than that first considered. It is very unlikely that a woman of irregular habits could produce two ova each capable of forming a healthy embryo.

3. The conception of mixed twins has been explained in the following way:—It is known that healthy spermatozoa may live for weeks in a woman’s Fallopian tube. Thus, the male ovum having been fertilised on the twelfth day or so after the first day of period, the female ovum may be fertilised by the same issue of spermatozoa some ten days later. This would also account for the smaller weight at birth of the girl. Any exception, where the girl was the finer specimen of the two, might be explained either by the arrested development of the male infant, owing to a less healthy male ovary, or by the cornu of the uterus on that side being less elastic and so preventing as full a development as that on the left side.

This last theory of conception, which has the support of many biologists, does not appear to me to be satisfactory. How can the fertilisation of the left ovum by the belated spermatozoa be really effective? And, if it is so, would not the lack of spontaneous vitality account for those arrested pregnancies one so often comes across, and for which, up to now, no cogent reason has been advanced? Faulty fertilisation might as well be the cause of an abortion at any early state of one embryo whilst the other continues its normal course.

I knew of one woman who, having had a mishap at thirteen weeks of a male fœtus, was surprised on getting up again to find that she was still pregnant. Five months later she gave birth to a healthy girl. Dr. Jameson cites the following case. A lady he attended was delivered on February 13 of a healthy male child, whom she nursed. On April 3, however she was taken ill, and shortly after was confined of a blighted fœtus, between eight and nine inches long. This fœtus was attached to a placenta, which appeared to be quite healthy, as large as that belonging to a full-grown one. Great numbers of such cases may be quoted, but till recently the causes have been obscure.

It is commonly believed that when twins are of mixed sex one or the other proves sterile when adult and there seems some ground for this assumption, but it is not of universal application.

Difficult as it was, I have made every effort to get at the facts, with the result that in scores of cases one or other of the twins has been found to have remained celibate, or, after marriage, to have had no children. I know of three sets only of mixed twins where both have married and had families.

The bearing of twins apparently tends to be hereditary in the female line, often recurring from mother to daughter, and this is more frequently the case where the twins are of the same sex. These are the result of a special development of one ovary or the other, accompanied by a propensity to discharge two ripe ova simultaneously.

Triplets, quadruplets, and quintuplets are likewise produced for similar reasons, as above described. In May, 1915, a Mrs. Howarth of Sheffield gave birth to three boys and one girl. They have all survived and done well. “An Italian woman at Palermo has given birth to five children, all of whom are in perfect health,” was an announcement which appeared in the papers not many months ago.

Such occurrences are quite tame compared to the account given by Ploss of an Italian woman, named Dorothea, who in two births produced twenty sons. First, a bevy of nine arrived, and two years later eleven more boys were born at one birth, these happenings being substantiated and vouched for by the doctors Francesco Pico della Mirandola and Ambrose Paré. The engraving, made from an authentic picture of this woman before the birth of her many sons, is most extraordinary to behold: the curious thing is that all were male children, so evidently the woman had a right ovary abnormally developed to the complete extinction of the left. Statistics go to prove, however, that the birth of female twins is more common than that of male. No doubt this is, in a measure, due to the greater difficulty of carrying male twins.

I knew of a woman who, within two years, gave birth to two sets of male twins; she subsequently bore first a single boy, and then a triplet of boys. Her left ovary had previously been removed, as the result of an unfortunate confinement when a girl-child was still-born; but she did not carry the first male twins longer than a bare thirty-three weeks. Had she carried them to their full term, it is doubtful whether she would have made a normal recovery and been able to produce the other six boys.

Those women always recover most easily from boy twins who do not carry them full time, and whose babies, when born, weigh barely from four to five pounds each. Twins weighing together twelve pounds or more at birth tend to overstrain the genital organs of the mother, with bad results. The tube is frequently left in a disastrously distended condition, which may lead to tubal pregnancies and appendix trouble.

Girl twins are seldom carried over eight months and are usually small, entailing infinitely less strain on the mother. They are not only more frequent, but easier to rear than boy twins. Mixed twins are the most usual of any, and they are rarely like each other, whether in looks or character. If they are very large, the result to the mother may subsequently be sterility, but this is not by any means to be taken as a general rule. I have known a woman start a fine family of six sons and six daughters with a good-sized set of mixed twins.

Mr. Rumley Dawson divides twins into four varieties:

Variety A. One Boy: One Girl: One from each ovary—a different Graafian follicle: a different ovum: generally one placenta to each.

Variety B. Two of the same sex: One ovary: two Graafian follicles: two ova: either two girls or two boys. In this variety there may or may not be a placenta to each, but generally there is only one.

Variety C. One Sex: one ovary: two ova contained in the same Graafian follicle. One corpus luteum only will ensue from the bursting of this Graafian follicle which contains two ovuli. In this case the children will resemble each other—far more closely than those coming under the first two categories. One placenta only will be found.

Variety D. One Sex: one ovary: one Graafian follicle and one ovum in which are contained two nuclei. These twins are rare, once in seven only. Extremely similar they are often joined together like the “Siamese Twins.” In triplets the same conditions obtain, and one ovum may produce three nuclei, all of the same sex.

As I have shown, twins are conceived according to all the rules laid down by the much-discussed, but hitherto imperfectly, understood, side-theory, and, where it was well-nigh impossible to explain clearly the conception of twins of mixed sex, complete understanding is now afforded by our newly acquired knowledge of the functioning of the left ovary.

That twins are the result of a peculiar condition of the ovary, usually hereditary, I have already indicated; it clearly follows therefore that multiple pregnancy cannot be initiated at the parental wish. But, where there is a marked family inclination to twins, it is certainly possible to ensure their being male or female, according to desire, provided they be both of the same sex.

XVII

“BEFORE OR AFTER”

“Count it crime to let a truth slip.”—BROWNING.

Hippocrates maintained that the male fœtus became animated thirty days after conception, while the female required forty-two days to become animate. This exactly bears out, and is explained by, the theory set out in my formula that a male conception occurs during certain days after the period, and a female somewhere between the twenty-first and twenty-eighth day: that is, eight to twelve days later.