The next stage is represented by this mass of cells forming themselves into a shape like a hollow ball. The third stage is the meeting of the two layers of cells, as if the ball had collapsed, and these two layers meet and unite as one, stretch and flatten out like a worm. After this stage things become more complicated; new organs begin to develop, line marks for the backbone and intestinal canal show themselves, as do the bony and muscular structure of the skeleton. A slight pulsation is observed, showing the development of the heart. The head fold is formed by a gradual bending of the spinal column at the front end of the ovum, which we will now call the embryo. There are also formed at this time, processes which soon become arms and legs, there is a furrow on the face, pits for the eyes; all of which has happened in less than four weeks. From this time forward development is rapid; the bones, which up to this time have been soft matter, grow harder, and all organs which were only outlined, [Illustration: FIG. II. Foetus in the Uterus at two months' pregnancy. ] now become definitely formed. At the end of the fourth month it has grown to its natural shape. The remaining months it increases in size and gains strength. The uterus becomes enlarged, rises out of the pelvis and occupies the abdominal cavity. It takes forty weeks or 280 days to complete the growth of the human embryo, although the time may be two weeks more or less and yet be normal. Let us see how the child has been fed all this time. When the ovum is fertilized and up to the eighth week it is fed by delicate branched threads, which form a covering for it. These threads are called “villi”, and dip into the uterine surface for nourishment from the mother to supply the embryo. About the eighth week these “villi” have grown greatly intertwined into a mass of spongy tissue full of blood vessels called the placenta (afterbirth). This fastens itself to one side of the uterus, takes oxygen as well as nutriment from the mother and sends it through the umbilical cord to the child, the point of attachment being at the navel, the depression left on the belly of the child by the cutting of the umbilical cord at birth. In the same way it takes the waste product from the child to the mother, and she, in turn, throws them out of her system through the kidneys, bowels and skin. The child and placenta are both encased within a membraneous sac, which secretes and serves to hold a watery fluid in which the child swims.