Blastodisc

**Definition:** A small whitish spot on the surface of the EGG YOLK where cleavage begins. Upon fertilization the cytoplasm streams from the vegetal pole away from the yolk to the animal pole where cleavage will occur. This germinal area eventually flattens into a layer of cells (BLASTODERM) that covers the yolk completely.

**Tree numbers:** - A16.331.042

**Synonyms:** - Germinal Area - Germinal Disc