It is about twelve days after conception before the impregnated ovule, which undergoes many changes during this time, makes its escape from the ovary where it became impregnated and enters one of the Fallopian tubes, thence gradually descending into the cavity of the womb. Here it begins to mature and become fitted for its birth into the outer world. Soon now the embryo (for such it is called at this early stage) begins to assume form. The first indication of formation that it is possible to discover, even by the help of the microscope, consists of an oblong figure, obtuse at one extremity, swollen in the middle, blunt-pointed at the other extremity. The rudimentary embryo is slightly curved forward, is of a grayish white color, of a gelatinous consistence, from two to four lines long and weighs one or two grains. A slight depression representing the neck, enables us to distinguish the head; the body is marked by a swollen centre, but there are as yet no traces of the extremities. So much can be observed about the end of the third week after conception. At about the _fifth week_ the embryo presents more distinctions. The head is very large in proportion to the rest of the body, the eyes are represented by two black spots, and the upper extremities by small protuberances on the sides of the trunk. The embryo at this stage is nearly two-thirds of an inch in length and weighs about fifteen grains. The lower extremities now begin to appear in the shape of two minute rounded tubercles. Till about this time a straight artery has been observed to beat with the regularity of the pulse; but now it appears doubled somewhat into the shape of an adult heart, although as yet it has but one auricle and one ventricle. As time advances we find the perfect heart with its two ventricles and two auricles, all developed from the original straight artery. At this period the lungs appear to exist in five or six different lobes and we can barely distinguish the bronchial tubes; about the same time the ears and face are distinctly outlined, and after awhile the nose is also faintly and imperfectly perceived. At about the _seventh week_ a little bony deposit is found in the lower jaw. The kidneys now begin to be formed, and a little later the genital organs. The embryo averages one inch in length. At _two months_ the rudiments of the extremities become more prominent. The forearm and hand can be distinguished but not the arm above the elbow; the hand is larger than the forearm, but is not supplied with fingers. The sex cannot yet be determined. The length of the embryo is from one inch and a half to two inches, and it weighs from three to five drachms. The eyes are discernible, but still uncovered by the rudimentary lids. The nose forms an obtuse eminence, the nostrils are rounded and separated, the mouth is gaping and the epidermis can be distinguished from the true skin.