* A _corpus luteum_ is a little yellowish body, formed in the ovary by changes that take place in the Graafian vesicle after it has burst and discharged its contents. _Corpora lutea_ were formerly considered a sure sign of impregnation, as they were thought to be developed only or chiefly in cases of pregnancy, but it is now known that they occur in all cases where a vesicle has been ruptured and an ovum discharged; though they attain a larger, size and are longer visible in the ovary when pregnancy takes place than when it does not.--G. R. "Harvey and DeGraaf dissected animals at most every period after coition for the express purpose of discovering the semen, but were never able to detect the smallest vestige of it in the uterus in any one instance."--Dewells Essay on Superfoetation. The fact of superfoetation furnishes a very strong argument against the idea that the semen enters the uterus in impregnation. A woman being impregnated while she is already impregnated constitutes superfoetation. It is established beyond a doubt that such instances have occurred, yet those who have supposed that it is necessary for the semen to pass through the mouth of the uterus to produce conception have urged that superfoetation could not take place, because, say they--and they say correctly--"so soon as impregnation shall have taken place, the _os uteri_ closes and becomes impervious to the semen ejected in subsequent acts of coition." Dr. Dewees related two cases, evidently cases of superfoetation, that occurred to his own personal knowledge. The first shows that, agreeable to the old theory, the semen must have met with other difficulties than a closed month of the uterus,--it must have passed through several membranes, as well as the waters surrounding the foetus, to have reached even the uterine extremity of a Fallopian tube. The second case I will give in his own words: "A white woman, servant to Mr. H., of Abington township, Montgomery county, was delivered about five and twenty years since of twins, one of which was perfectly white, the other perfectly black. When I resided in that neighborhood I was in the habit of seeing them almost daily and also had frequent conversations with Mrs. H. respecting them. She was present at their birth, so that no possible deception could have been practiced respecting them. The white girl is delicate, fair-skinned, light-haired and blue eyed, and is said very much to resemble the mother. The other has all the characteristic marks of the African; short of stature, flat, broad-nosed, thick-lipped, woolly-headed, flat-footed, and projecting heels; she is said to resemble a negro they had on the farm, but with whom the woman would never acknowledge an intimacy; but of this there was no doubt, as both he and the white man, with whom her connection was detected, ran from the neighborhood as soon as it was known the girl was with child."