Fig. [58]. —Passage of spermatozoon through the zona pellucida of the ovum of asterakanthion.
Fig. [59].—Ovum of scorpæna scrofa thirty-five minutes after fertilization.
Fig. [60].—Male pro-nucleus and female pro-nucleus in fertilized ovum of frog, prior to the formation of the segmentation nucleus.
Hippocrates writes: Hae nempe post menstruam purgationem utero concipat. Aristotle says: Plerasque post mensum fluxum nonnullas vero fluentibus adhuc menstruis. Galen writes: Hoc autem conceptionis tempus est vel incipientibus vel cessantibus menstruis.
Soranus writes to a similar effect: Just as the soil is suitable only at certain seasons for the reception of the seed, so also in the human race intercourse does not always take place at a time suited for the reception of the semen. To be effective, coitus must occur at the proper time.... The act of intercourse that is to lead to conception may best occur either just before or just after the menstrual flow, when, moreover, there is strong desire for the sexual embrace, and neither when the body is fasting, nor when it is full of drink and undigested food. The time before menstruation is, however, unsuitable, for then the womb is heavy from the flow of blood, and two conflicting tendencies will come into operation, one for the absorption of material and the other for its outflow. During menstruation, again, conception is unlikely to occur, for then the semen is wetted and washed away by the flowing blood. The sole proper time is that immediately after the flow, when the womb has freed itself from its humours, and warmth and moisture stand in harmonious relationship.
Among many of the castes of Hindustan, it is a religious ordinance that on the fourth day of menstruation a man shall have intercourse with his wife, “since this day is that on which conception is most likely to occur.” Indian physicians advise, in order to bring about conception, “that coitus be effected always as soon as the menstrual flow has ceased, at the end of the day, and when the lotus has closed.” In Japan, medical opinion is to the effect that a woman is capable of conceiving during the first ten days after menstruation, but not later (Ploss and Bartels).
The view that the first days of the intermenstrual interval are those most favourable to the occurrence of conception, is further confirmed by the statistical data collected by Löwenfeld, Ahlfeld, Hecker, and Veit; and it appears that as the date of the next menstruation is approached, there is a continual decline in the frequency of conception; just before the flow, conception hardly ever occurs. Hensen, from the records of 248 conceptions in which the date of the fruitful intercourse was exactly known, draws the following conclusions: