As gestation progresses the texture of the uterus changes. The peritoneum spreads out in all directions without a decrease in thickness; the mucous coat becomes apparent, it grows redder and more vascular, and its folds disappear; the glands of the body of the womb grow longer; the middle coat is enlarged by the increase in size of always existing muscular elements, and the formation of new fibres and increased connective tissue. There is, towards the end of pregnancy, an astonishing development of the vascular system; the lymphatic vessels acquire considerable calibre, and the nerves are developed in every way, although the neurilemma is most affected. The changes developed in the uterine mucous membrane are of especial interest. Its vascularity is greatly increased during menstruation, the glands are enlarged, the membrane thickened, thrown into folds and becomes of a violet color; this condition continuing until the ovule is discharged, or until the last of the menstrual period. The fecundation of the ovum will maintain and increase this vascular condition of the membrane. Its vessels are so enlarged as to cause small effusions beneath the epithelium, which gives to the internal surface a spotted appearance; after two or three weeks it is still more mottled, more puffed up, and furrowed with folds and wrinkles. This membrane is the _decidua_, which is afterwards expelled, with other contents of the uterine cavity. The DECIDUA REFLEXA is a fold of the decidua in which the fœtus is enveloped, and both of these membranes, which are at the last expelled with the fœtus, are developed from the uterine mucous membrane. The uterine decidua, after the second month, grows thinner, and its folds are gradually effaced; after the fifth month it is only one twenty-fifth of an inch in thickness, and it is still thinner at the termination of pregnancy. At the fifth month it is separable from the uterus, and the first trace of the new membrane which is to replace the decidua may be detected under it. A partly uterine membrane may be thrown off when an abortion occurs, during the early months of pregnancy. CHAPTER VII. THE OVUM AND ITS DEVELOPMENT. The ovum at maturity (and not impregnated) is described as being composed of the vitelline membrane, which seems like albumen in appearance, but is a thick, transparent membrane, without determinate texture; second of the vitellus or yolk, a granular liquid contained in the vitelline membrane, composed of a coherent transparent viscid mass; third of the germinal vesicle, which is composed of a transparent colorless membrane, enclosing a liquid also transparent; and lastly, of the germinal spot, that is held in suspension in the liquid that the germinal vesicle contains.