The meaning of the word puberty is maturity. It is the period at which the girl and the boy reach sexual maturity; in other words, the period at which the sex glands of the boy begin to generate spermatozoa, and the sex glands of the girl begin to mature and expel eggs or ova; with the girl puberty is marked by an additional phenomenon, which has no analogue in the boy, namely, menstruation. =Physical Changes.= The word puberty is derived from the word _puber_, which in Latin means mature, ripe. But the word puber is itself derived from the word _pubes_, which in Latin means fine hair or down. For at this period of maturity all mammals (that is animals which have breasts and nurse their young) begin to develop a growth of hair. You know that our entire body, with the exception of the palms of the hands and the soles of the feet, is covered with innumerable hair follicles, and from our birth our entire body, with the exception named, is covered with fine hair. The hair may be too delicate to be seen, but it is there, and with a magnifying glass you can see it without any trouble. But at puberty the hair increases in thickness and in quantity, and becomes abundant in places where it was hardly noticeable before--the upper lip and face in boys, and the armpits and lower part of the abdomen in both boys and girls. And so the first apparent physical sign of puberty in a girl is the gradual appearance of hair in the armpits, on the mons Veneris and the labia majora. But all the genital organs are undergoing rapid development; the vulva, the vagina, the uterus and the ovaries become larger, and the ovaries which up to that time were elaborating an internal secretion only, now also begin to manufacture ova; in other words, the monthly process of ovulation is begun. Synchronously with the process of ovulation, there commences the monthly function of menstruation. The breasts also increase in size, assume the characteristic contour, develop their glandular substance, and become capable of secreting milk for the use of any possible offspring. During this period of development they are often very sensitive to the touch or feel painful without being touched. But not only the genital organs undergo growth and development--the entire body participates in the process. The growth in height is the most rapid at this period; the greatest growth takes place in the limbs--legs and arms. The pelvis becomes broader, and the chest or thorax also becomes broader and larger. The muscles become larger and rounder and finally give the girl the beautiful womanly form.