Final answer:
The initial reproductive structures of male and female embryos are the same until the seventh week of gestation, after which sexual differentiation begins and distinct male and female genitals develop.
Step-by-step explanation:
The initial reproductive structures of male and female embryos appear the same until approximately the seventh week of gestation. This is because embryonic development features a stage where the external genitalia are apparent, yet male and female embryos are indistinguishable. It is not until the fetal stage, specifically during weeks 9-12, that sexual differentiation takes place and male and female genitals start to develop distinctly.