The Stages of Growth.--At first insignificant in size--a simple cell, the embryonic human being steadily increases in size, gradually approximating more and more closely to the human form, until, at the end of about nine calendar months or ten lunar months, the new individual is prepared to enter the world and begin a more independent course of life. The following condensation of a summary quoted by Dr. Austin Flint, Jr., will give an idea of the size of the developing being at different periods, and the rate of progress:-- At the end of the third week, the embryon is a little less than one-fourth of an inch in length. At the end of the seventh week, it is three-fourths of an inch long. The liver, lungs, and other internal organs are partially formed. At the eighth week, it is about one inch in length. It begins to look some like a human being, but it is impossible to determine the sex. At the third month, the embryon has attained the length of two to two and one-half inches. Its weight is about one ounce. At the end of the fourth month, the embryon is called a fetus. It is from four to five inches long, and weighs five ounces. At the fifth month, the fetus is nearly a foot long, and weighs about half a pound. At the sixth month, the average length of the fetus is about thirteen inches, and its weight one and a half to two pounds. If born, life could continue a few minutes. At the seventh month, the fetus is from fourteen to fifteen inches long, and weighs two to three pounds. It is now viable (may live if born). At the eighth month, the length of the fetus is from fifteen to sixteen inches, and its weight from three to four pounds. At the ninth month, the fetus is about seventeen inches long, and weighs from five to six pounds. At birth, the infant weighs a little more than seven pounds, the usual range being from four to ten pounds, though these limits are sometimes exceeded. Duration of Gestation.--The length of time required for the development of a human being is usually reckoned as about forty weeks. A more precise statement places it at about two hundred and seventy-eight days. This limit is often varied from. Cases have occurred in which a much longer time has been required, and numberless cases have occurred in which human beings have been born several weeks before the expiration of the usual time, as stated. There is some uncertainty respecting the exact length of the period of gestation, which grows out of the difficulty of determining, in many cases, the exact time when conception takes place.