There are two peculiarities of the human species respecting conception which I will notice. First, unlike other animals they are liable, and for what has been proved to the contrary, equally liable--to conceive at all seasons of the year. Second, a woman rarely, if ever, conceives until after having several sexual connections; nor does one connection in fifty cause conception in the matrimonial state, where the husband and wife live together uninterruptedly. Public women rarely conceive, owing probably to a weakened state of the genital system, induced by too frequent and promiscuous intercourse. It is universally agreed, that some time after a fruitful connection, a vesicle (two in case of twins) of one or the other ovary becomes so enlarged that it bursts forth from the ovary and takes the name of ovum, which is taken up, or rather received, as it bursts forth, by the fimbriated extremity of the Fallopian tube, and is then conducted along the tube into the uterus, to the inner surface of which it attaches itself.* * Since Dr. Knowlton's work was written, the very important fact has been discovered that ova are periodically discharged from the ovaries in the human female and other animals, not in consequence of fruitful connection having taken place, as was formerly believed, but quite independently of intercourse with the male. Such a discharge of ova occurs in the lower animals at the time of heat or rut, and in women during menstruation. At each menstrual period, a Graafian vesicle becomes enlarged, bursts, and lets the ovum which it contains escape into the Fallopian tube, along which it passes to the uterus. "It has long been known," says Dr. Kirke, "that in the so-called oviparous animals, the separation of ova from the ovary may take place independently of impregnation by the male, or even of sexual union. And it is now established that a like maturation and discharge of ova, independently of coition, occurs in Mammalia, the periods at which the matured ova are separated from the ovaries and received into the Fallopian tubes being indicated in the lower Mammalia by the phenomena of _heat_ or _rut_; in the human female by the phenomena of _menstruation_. Sexual desire manifests itself in the human female to a greater degree at these periods, and in the female of mammiferous animals at no other time. If the union of the sexes takes place, the ovum may be fecundated, and if no union occur, it perishes. From what has been said it may therefore be concluded that the two states, heat and menstruation, are analogous, and that the essential accompaniment of both is the maturation and extrusion of ova."--"Handbook of Physiology," page 724.--G. R.