The ovule, after it arrives in the uterine cavity, comes in contact at all points with the mucous membrane of the uterus. Its nutrition at first is organic by superficial imbibition; afterwards, probably the villi of the chorion imbibe the fluids there secreted, and transmit them into the space between the chorion and the amnion, thence it transcends through the walls of the amnion, and a portion is conveyed into the fœtus through the umbilical vesicle. After the placenta is formed there may still be some absorption of some of the nutritive matters contained in the liquor amnii through the skin of the fœtus, but its growth is principally maintained by an assimilation of that which the radicles of the umbilical vessels take up in the placenta. By means of the extensive contact existing between the vascular apparatus of the two placentas, a transudation probably takes place of some part of the maternal blood, which is absorbed and mingled with the fœtal blood, and furnishes some of the nutritive material. When mingled with the fœtal blood, the nutritive elements supplied by the mother are devoted to the development of the organs. It is supposed, however, that they undergo changes in the large liver of the fœtus and in its intestines. There is no true respiration in the uterine cavity, but one function of the placenta is to renew the blood of the fœtus from that of the mother, in about the same way that the blood of fishes is ærated by the water passing through the gills. Whether in the earlier months absorption is carried on by the surface alone, or whether a portion of the liquor amnii finds its way to the stomach is difficult to decide, but, without doubt, a certain amount of digestion is carried on. The CIRCULATION of the blood in the fœtus cannot be understood without referring to certain anatomical peculiarities that do not exist in the adult. These characteristics depend on the absence of respiration, and disappear when it is established. 1st. The septum between the auricles of the heart is imperfect, having in its center a valvular oval aperture called the _foramen ovale_. 2d. The pulmonary artery, soon after its origin, gives off a branch, the _ductus arteriosis_, which enters the aorta just below the arch. The pulmonary arteries are very small. 3d. The _umbilical artery_ in the _fœtus_ is a large vascular trunk, which is nearly obliterated in after life. The two umbilical arteries run forwards and inwards along the lateral and superior parts of the bladder, then curve forwards to the abdominal wall, along which they ascend to the umbilicus, then pass along the cord to the placenta.