Segmentation of the vitellus—a sure sign of fecundation—does not occur (at least in birds) until the arrival of the ovum in that part of the tube where the shell forms.
Fecundation does not occur in the uterus, as Pouchet said, but higher up. But, according to Van Beneden and Ch. Robin, the spermatozoa can, in some animals, penetrate the ovules in anticipation, and remain living therein, (as in the copulatory pouches of certain invertebrata, etc.,) wait ing for the ovule to arrive at maturity, or to undergo molecular changes from nutritive processes.
In woman, the spermatozoa, which have reached the tube before men struation, remain there during the menses, and fecundate the ovum as soon as the follicle ruptures. The uterine flow immediately ceases (Robin). Fecundation, then, cannot have occurred until 10 or 20 hours after the close of menstruation, supposing coition to have occurred directly the flow has ceased. Hence, coition preceding the flow, produces spermatozoa which fecundate after the flow has ceased.
Bischoff states that the ovule is capable of fecundation for 10 or 12 days, thus explaining how, in some women, impregnation seems to occur mid way between the menstrual periods.
Of the phenomena of fecundation, Ch. Robin mentions not only dissolu tion but liquefaction of the spermatozoa in the ovule; that is to say, mole cular modification causing dissolution of its molecules, which finally unite with the substance of the vitellus.
A new being is to grow from this, and, from the transformation, comes original or incarnated heredity that may recur in later impregnation. Hence the well-known idea that the alteration of a species may depend upon the first contact with a debased race; and also, that mares, or bitches, of good stock, once impregnated by the male of a common breed, will, for a long while after, give birth to common stock, even if they have been covered by the highest bred males. Widows, remarrying, have had chil dren who resembled the first husband.