At approximately day 1

Primary sex cords grow into the underlying mesenchyme. The gonad now consists of an external cortex and internal medulla. The cortex eventually regresses as the testis develops.

Duration: 1 week

Reference

Moore KL, Persaud TVN. 1998. The Developing Human: Clinically Oriented Embryology. 6th ed. Philadelphia: WB Saunders Co.

At approximately day 1

External genitalia differentiate to form penis and scrotum.

Reference

Larsen WJ. 1997. Human Embryology. New York: Churchill Livingstone Inc.