The author gave a brief sketch of the various theories which have been advanced by Velpeau, R. Lee, Braxton Hicks, the Hunters, Owen, Weber, J. Reid, J. Goodsir, Virchow, Kölliker, Van Der Kolk, Arthur Farre, and Ercolani regarding to the relations of the maternal blood-vessels to the placenta and chorionic villi. He then proceeded to state the results of his own observations on various specimens of placentæ, some of which had been separated at the full time, others prematurely, and on three specimens attached to the uterine wall.