Explanation

In Ascidian embryos, the grey crescent gives rise to the notochord. 

The gray crescent:

• In ascidian development, the gray crescent is a region of pigmented cytoplasm located at the posterior of the fertilized egg.
• It is important for determining the future location of the notochord and neural tube. 

Notochord formation:

• The cells derived from the gray crescent are specifically destined to form the notochord, a rod-like structure that provides structural support during development.