Biology of Finfish and Shellfish

4.11.2. Ontogeny of Sepia

One blastoderm grows very slowly round the yolk so that after long time all the outer organs of the embryo are quite recognisable in the region of the original germinal disc; the opposite pole is still occupied by the yolk. Two germinal layers lies in such a way that the centre of the germinal disc or animal pole is placed dorsally, and corresponds with the uppermost point of the visceral dome of the adult animal, while the mass of nutritive yolk lies ventrally.