Grey crescent is the area.

The Grey crescent is the area of the region opposite the sperm entrance that formed a melanin-rich place:

1. There are two poles present in the frog's zygote.
2. There are two poles: vegetal and animal.
3. The grey crescent, which is rich in melanin, separates these two.
4. The broadest part of the grey crescent forms the dorsal end.
5. The grey crescent helps in establishing polarity.