The term "the embryo" is employed to designate the developing young creature in the earlier stages of its development, particularly before the end of the third month of its existence. After the end of the third month the embryo is called "the fetus." In the short space of 280 days the young creature evolves and develops from a single simple cell into a complex organism--a perfect miniature human being. Nature works a wonderful miracle here, and yet so common is it that we take it all as a matter of course, and lose sight of the miracle. From the most simple forms are formed in the developing creature the most complex organs and parts. The heart is formed from a tiny straight line of cells, by enlargement and partition. The stomach and intestines, likewise, develop from a tiny straight line of cells arranged as a tiny tube--the stomach is formed by dilation of one part of the tube, while the large intestine experiences a similar though lesser distention and a greater growth in length; the smaller intestines being formed by growth in length and circumference. The other organs evolve from similar simple beginnings. The embryo is nourished during its earlier stages by means of the "yolk sack," or "umbilical vesicle," which is outside the body of the embryo, being joined to it by means of the umbilical duct. This yolk sack (originally formed by a "drawing together" in the ovum, which thus separates itself into two portions or areas) is an important feature of the life of the embryo, as it nourishes and sustains it in its earlier stages. Blood vessels form in this yolk sack, and after a time its fluid is absorbed, and after the third month the sack gradually disappears. After the passing away of the yolk sack, the embryo is nourished and sustained by the "allantois," another peculiar sack which is formed. This sack readily becomes filled with blood-vessels, and serves to nourish the embryo by sustenance obtained from the body of the mother through the walls of the Uterus, a direct communication with the blood-vessels of the mother thus being secured. The blood in the embryo, and that in the mother, come into close contact, thus allowing the embryo to be nourished by the blood of the mother. After a time, in turn, the allantois diminishes and dwindles away, its offices being taken up and performed by the "placenta" or "afterbirth." THE PLACENTA OR AFTERBIRTH. The Placenta, or afterbirth, is a round, flat substance or organ, contained within the Uterus, by which communication and connection is established and maintained between the fetus and the mother, by means of the umbillical cord. It is a flat, circular mass, about seven inches in diameter, and weighing about sixteen ounces. It is attached to the sides of the Uterus of the mother during the period of gestation, and is expelled from the body of the mother, as "the afterbirth," after the birth of the child.