In girls, pubic hair begins to grow, followed by underarm hair; breasts develop, with the areola around the nipple becoming darker. Fat deposits around the hips and buttocks also contribute to the female's more rounded appearance. Although the menstrual cycle begins, it may be irregular, with some monthly cycles occurring without ovulation. Since 1840, menstruation has been beginning a few months earlier every decade, possibly due to better nutrition or to the consumption of meat that contains hormones. In general, girls gain less height and weight than boys do during their teenage years.
Penis : This is the male organ used in sexual intercourse. It has three parts: the root, which attaches to the wall of the abdomen ; the body, or shaft; and the glans, which is the cone-shaped part at the end of the penis. The glans, also called the head of the penis, is covered with a loose layer of skin called foreskin. This skin is sometimes removed in a procedure called circumcision . The opening of the urethra, the tube that transports semen and urine, is at the tip of the penis. The glans of the penis also contains a number of sensitive nerve endings.