The formation of male tubular genitalia is directed by the hormones secreted by the developing testes. The secretion of testosterone from the Leydig cells and paramesonephric inhibitory hormone from the Sertoli cells induce the differentiation of the Wolffian body (mesonephros) and the Wolffian ducts (mesonephric ducts) (refer back to chapter 12). Paramesonephric inhibitory hormone inhibits the development of the paramesonephric ducts (Muellarian ducts). In the absence of developing testes and the presence of estrogens, the paramesonephric ducts develop into the uterus, uterine tubes and cranial vagina. Estrogen also stimulates the development of female external genitalia, the caudal vagina, the vestibule and the clitoris.