Formation of return to the ovum. We have seen that after conception it divides into two cells, then into four, and so on, till a mass of cells is produced, which dis pose themselves in such a way that a hollow sphere is formed. It is from the outer layer of this sphere that the shaggy projections are thrown out which become connected with the part of the wall of the womb that has covered over the ovum, forming an outer membrane. On a part of the sphere the embryo begins to develop, and as it grows the parts of the sphere beyond the place where it is developing rise up round it, and finally meet and close over it. Thus the embryo conies to be enclosed within a membranous sac of its own, called the amnion, while it maintains its connection with the parts beyond by a cord, the umbilical cord. As the embryo grows, fluid is formed within the sac, and thus the embryo, as early as the second month, is floating in fluid contained within a sac, and connected with the wall of the mother's womb by means of a cord and the placenta. With further accumulation of fluid the anmion enlarges till it conies into contact with the outer membrane already mentioned, with which it becomes fused. So in the later stages of pregnancy the foetus is freely movable in a mass of liquid contained within a large sac formed of the blended membranes, and is suspended in the liquid by the cord, the other end of which is attached to the placenta, which is in close connection with the wall of the womb, the womb itself being completely filled by the sac and its contents. In the course of labour the membranes are ruptured and the liquid escapes, in common talk, "the waters break".
Progress of Growth at Different Months.
—In the course of the third month of preg nancy, the ovum, with its growing embryo en closed within its membranes and floating in the fluid, comes to occupy the whole cavity of the womb. As the embryo continues growing the womb must needs enlarge with it.
After the end of the third month of pregnancy the growing offspring is called a fcetus, and is so called till birth takes place.
At this time the fcetus measures from 5 to E inches in length, and weighs about 4 ounces. Already at this time the sex is distinct, tin outline of the body is complete, the eyes and ears are formed, and the nails have commenced to form.
At the end of the fourth month the fcetin has increased to 7 inches in length, and nearl 9 ounces in weight. A slight down, instead of hair, begins to appear on the scalp and surface of the body, and brisk movements occur, though they may not yet be felt by the mother.
With the end of the fifth month the length has increased to from 8 to 10 inches, and th, weight from 10 to 12 ounces. Early in the fifth month the first movement is usually de tected by the mother, and this is called thy period of quickening, though, as has alread: been said, this is only the time when the mother feels the movement, which has previously oc curred unperceived by her.
At six months the growing child is 11 to 12 inches long, and weighs more than a pound. The nails are solid, and eyebrows and eyelashes have begun to form.
In the course of the seventh month the length increases•to from 12i to 14 inches, and the weight is considerably increased by deposit of fat under the skin. In the male Lhild the testicles begin to descend from the cavity of the belly towards their proper position.
By the end of the eighth month the length of the child is usually about 17 inches, and the weight 4 to tsi pounds. The skin is red and covered , with down. In the male child one testicle Ters completely descended, usually that of the left side.
Size and Weight of Child at birth the average length is from 19 to 24 inches, and the average weight 7 pounds.
Male children are usually larger than female children. While 7 pounds is an average weight, there are many variations. 5i to 6 pounds weight means a very small child, and 12 to 13 a very large child, but such extremes are now and again met with.