This period, which indicates, by the feelings and ideas, the desires and will, that the subjects are capable of procreation, is called _puberty_. The mind acquires new and more delicate perceptions, the person becomes plumper, the mammæ enlarge, and there is grace and perfection in every movement, a conscious completeness for those relations of life for which this function prepares them. The period of puberty is also indicated by MENSTRUATION. The catamenial discharge naturally follows the ripening and liberation of an ovum, and as the ovaries furnish one of these each month, this monthly flow is termed the _menses_ (the plural of the Latin word _mensis_, which signifies a month). The menstrual flow continues from three to five days, and is merely the exudation of ordinary venous blood through the mucous lining of the cavity of the uterus. At this time, the nervous system of females is much more sensitive, and from the fact that there is greater aptitude to conception immediately before and after this period, it is supposed that the sexual feeling is then the strongest. When impregnation occurs immediately before the appearance of the menses, their duration is generally shortened, but not sufficiently to establish the suspicion that conception has taken place. The germ is the contribution of the female, which provides the conditions which only require the vivifying principle of the sperm for the development of another being. The period of aptitude for conception terminates at the time both ovulation and menstruation cease, which, unless brought about earlier by disease, usually occurs about the forty-fifth year of her age. FECUNDATION.