The male and female reproductive systems follow a similar pattern of development, with sexual distinction coming about as a result of the influence of hormones. As mentioned previously, the reproductive organs of both sexes derive from the same developmental tissue and are considered homologous.

The first sign of development of reproductive organs (male or female) occurs during the fifth week with the formation of the gonadal ridge. The gonadal ridge continues to grow behind the developing peritoneal membrane lining the abdominal cavity. By the sixth week, stringlike masses called primary sex cords form within the enlarging gonadal ridge. The primary sex cords in the male will eventually mature to become the sperm-nurturing seminiferous tubules. In the female, the primary sex cords will contribute to nurturing tissue of developing ova.

Each gonad develops near a mesonephric duct and a paramesonephric duct. In the male embryo, each testis connects through a series of tubules to the mesonephric duct. During further development, the connecting tubules become the seminiferous tubules, and the mesonephric duct becomes the efferent ductules, epididymis, ductus deferens, ejaculatory duct, and the seminal vesicle. The paramesonephric duct in the male degenerates without contributing any functional structures to the reproductive system.

In the female embryo, the mesonephric duct degenerates, and the paramesonephric duct contributes greatly to structure of the female reproductive system. The distal ends of the paired paramesonephric ducts fuse to form the vagina and uterus. The proximal unfused portions become the uterine tubes.

By the sixth week, a swelling called the genital tubercle is apparent in the groin of the embryo. The mesonephric and paramesonephric ducts open to the outside through the genital tubercle. The genital tubercle consists of a glans, a urethral groove, paired urethral folds, and paired labioscrotal swellings. As the glans portion of the genital tubercle enlarges, it becomes known as the phallus.

Early in fetal development (the tenth thought the twelfth week), sexual distinction of the external genitalia becomes apparent. In the male, the phallus enlarges and develops into the glans of the penis. The urethral folds fuse around the urethra and become the erectile tissue that forms the body of the penis. The labioscrotal swellings fuse to form the scrotum, into which the testes will descend. In the female, the phallus gives rise to the clitoris, the urethral folds remain separated as the labia minora, and the urethral groove is retained as a longitudinal cleft known as the vestibule.

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