The puppies of a bitch, we have already mentioned, generally bear a resemblance to more than one of the dogs with which she has had connexion during the period of heat, and this period may extend to eight or nine days. A mare, which had been covered by a stallion, was five days afterwards covered by an ass, and bore at the usual time twins, one of which was a common foal, the other a mule" Women have been known to bear two chil dren of different colour; and in one of these instances the mother is said to have confessed to having admitted the embraces of a black servant a few hours after her husband, who was white.
Facts like these seem to shew that sexual intercourse limited to an interval of a few days (most probably before the uterus has been closed by the decidua) may produce super fcetation. But we would remark that, although it may be that the mechanical obstruction of the decidua opposes an obstacle to the passage of semen upwards, or the descent of a new ovum into the uterus, there is obviously ano ther cause why superfcetation should not occur : we mean that fundamental change in the con stitution which is induced by pregnancy, similar to that which continues in the majority of women during lactation. But for such a constitutional change, we conceive continual derangement of the function of utero-gestation would attend that process in consequence of the recurrence of some of the more general symptoms of conception, even although a lodgement of a new ovum in the cavity of the uterus were impossible.
The following cases serve to illustrate the nature of the more important facts on record which do not admit of an explanation, except ing on the supposition that superfcetation has taken place.
1. A woman bearing a full-grown male child had neither lochia nor milk after its birth, and a hundred and thirty-nine days afterwards bore a second child—a living girl, when the milk and lochia came naturally. Eisenmann, who had observed this case, explained the occurrence by supposing that a double uterus existed; but upon the woman's death some time afterwards, no unusual structure was found.-1 2. Desgranges observed another instance in which a woman bore two girls at the interval of a hundred and sixty-eight days in the same circumstances as in the above-mentioned case.* 3. A third case is related by Fournier in two girls were born at the interval of five months, there being lochia for a few days after the birth of the first.} 4. A fourth instance is mentioned of two children born at the interval of a hundred and nine days.! 5. Velpeau relates that a Mad. Bigaux had first a living child, and four and a half months, or a hundred and forty days afterwards, a second, also alive.§
We confess that we think these cases, if correctly reported, go far to prove the possible occasional occurrence of superfcetation in the human species. On the supposition that two children born alive at different periods remote from one another have been conceived at the same time, three months appears to be the greatest extent to which the interval between their births could reach, the first being born prematurely at six and a half or seven months, and the second being retained in the uterus till the period of nine and a half or ten months; but this is improbable in some of the instances before us, as both children appeared equally complete, and no mere difference in the rate of their growth could account for their birth at so remote periods.
We are reduced then to the necessity of ad mitting the possibility, in very rare instances, of superfcetation ; but at the same time we may remark that the evidence regarding it is not sufficiently precise, and we are left entirely at a loss to explain what causes may give rise to this variation, and in what manner the seminal fluid may be supposed to pass through the uterus, or the new ovum to gain an entrance there.
§ 2. exerted by parents on the qualities of their offspring in generation.— One of the most obvious and important laws of the reproductive function is that by which the specific distinction of animals is preserved. Like produces like; and for the most part an undeviating succession of generations of simi lar structure and qualities prevents both the extinction of any species and its being blended with or lost in any other. Numerous examples will recur to the mind of every one, of striking family resemblance, which point out in how many respects children frequently inherit their qualities from their parents ; but it must be held in remembrance that family or hereditary resemblance is seldom if ever complete, but only of that more general kind which belongs to the species. Thus in one fiunily we re cognise numerous minute differences, and in fact it may be said that there are scarcely any two individuals of the same or of different family exactly alike. In respect to sex, the most obvious difference exists: the mother producing male and female; the son is not an exact copy of his father, nor the daughter of her mother, nor are they a mixture of both ; but each of them bears certain resemblances to one or other or to both of the parents, into which it may be interesting to inquire,—an in vestigation which is to be regarded of some practical importance in reference to the breed ing of cattle and other stock.