These slides, with the attached eggs and larvae, are then easily manipulated for study. The eggs are yellowish in color and measure about 70 microns in diameter. Maturation apparently takes place before shedding, since polar bodies are not found on shed eggs. Cleavage is total and equal. At the 8-cell stage, there is a rotation of some of the blastomeres to form a flat plate of cells.
Continued cleavage gives rise to a hollow blastula consisting of a single layer of cells.
These cells develop cilia and, while the blastula is still rotating within its membrane, the endoderm is formed by multipolar delamination. With the formation of this inner layer the blastocoele is eliminated. At this time the planulae are bottom-swimmers. The coelenteron begins to form in the posterior portion of the larva by a rearrangement of the endoderm cells, shortly before metamorphosis. At metamorphosis the larva stops swimming, loses its cilia, and attaches by the broad anterior end.