Abortion or miscarriage is known by every woman to consist of the premature expulsion of the product of conception. It is not as well known, however, if the statements of patients are to be relied upon, that this product of conception is in reality endowed with vitality from the moment of conception itself. It is important, therefore, to decide in what the moment of conception consists. It has now been ascertained that every variety of animal life originates from an egg, even primarily those lowest forms in which occur the phenomena of so-called alternate generation; in each and every one of them, mammals or invertebrates, the origin is from as distinct an egg as is laid by bird, tortoise, or fish; the human species being no exception to this general rule. Before this egg has left the woman's ovary, before impregnation has been effected, it may perhaps be considered as a part and parcel of herself, but not afterwards. When it has reached the womb, that nest provided for the little one by kindly nature, it has assumed a separate and independent existence, though still dependent upon the mother for subsistence. For this end the embryo is again attached to its parent's person, temporarily only, although so intimately that it may become nourished from her blood, just as months afterwards it is from the milk her breasts afford. This is no fanciful analogy; its truth is proved by countless facts. In the kangaroo, for instance, the offspring is born into the world at an extremely early stage of development, "resembling an earthworm in its color and semi-transparent integument,"[10] and then is placed by the mother in an external, abdominal, or marsupial pouch, to portions of which corresponding, so far as function goes, at once to teats and to the uterine sinuses, these embryos cling by an almost vascular connection, until they are sufficiently advanced to bear detachment, or in reality to be born. The first impregnation of the egg, whether in man or in kangaroo, is the birth of the offspring to life; its emergence into the outside world for wholly separate existence is, for one as for the other, but an accident in time. It has been asserted by some authors, as by Meigs, that conception is only coincident with the attachment of the impregnated egg to the uterine cavity for its temporary abode therein, or, in exceptional cases, as in extra-uterine pregnancy so called, with its attachment to some other tissue of the mother; thereby attempting to establish a difference between impregnation and conception; a difference that is at once philosophically unfounded, and plainly disproved by all analogical evidence, as the fact, for instance, that in most fishes impregnation occurs entirely external to the body of the mother, from which the ova had previously, or during the process of copulation, permanently been discharged.