The five stages of male genital development. Stage 1 shows the undeveloped genitals of childhood. In Stage 2, pubic hair growth begins and the testicles begin to enlarge. By Stage 3, the penis grows longer and wider. The testicles continue to enlarge. In Stage 4, the penis and testicles continue to enlarge while the head of the penis becomes more developed. In Stage 5, the genitals have become their adult size, and pubic hair covers the region. (Illustration by GGS Information Services.)