The primitive sex cords, now called testis cords, have grown
over the past few weeks, extending into the surrounding
tissue. The cords now fuse together to form a network that
will later connect the Wolffian duct to the developing
testes.
Cells in the area secrete hormones, including testosterone.
The hormones cause the degeneration of the Mullerian duct
(which will continue to develop in the female) and the
external genitalia to develop into a penis. The hormones
also signal other areas throughout the body to develop male
characteristics.
