When the female infant is born, her ovaries contain as many ova or eggs as they ever will contain. In fact, they contain more than they will at puberty. For it is estimated that at birth each ovary contains about 100,000 oval the majority of these, however, disappear so that at the age of puberty each ovary contains only about 30,000 ova. As only one ovum ripens each month from the time of puberty to the time of the menopause (i.e., about 300 to 400 ova at the utmost during a lifetime), and as only a dozen or two ova would be necessary for the propagation of the race, it seems a superabundance of ova, an unnecessary lavishness. But nature is lavish where the propagation of the species is concerned. A portion of an ovary or of both ovaries might become diseased, and thousands of ova might become unfit for fertilization; nature therefore puts in an extra reserve supply. We see a still more striking example of this extreme extravagant lavishness in man; only one spermatozoon is necessary to impregnate the ovum, and only one spermatozoon can penetrate the ovum; nevertheless each normal ejaculation of semen contains between a quarter and half a million spermatozoa.