SUPERFETATION, in medicine, a second or after-conception, happening when the mother, already pregnant, conceives of a latter coition; so that she bears at once two fetuses of unequal age and bulk, and is delivered of them at different times. We meet with instances of superfetations in Hippocrates, Avistotle, Du Laurens, &c.: but they are said to be much more frequent in hares and fows. Naturalists hold, that female rats are frequently born with young rats in their wombs; and we are told of extraordinary instances of this kind in the female part of the human species,
Superficies species, by Bartholine, Mentzelius, and in the history of the Royal Academy of Arts and Sciences.