The egg is faintly pink in color, granular and almost opaque. It is homolecithal. The eggs are embedded in large, irregular jelly-masses. Cleavage is unequal and spiral, and the micromeres are relatively large. No polar lobes are formed.
Gastrulation is by a combination of invagination and epiboly.
Time is calculated from shedding of the eggs. At this time, there is a single pair of eyespots in the pre-trochal region. The hatched larvae have three to five pairs of setigerous segments and an additional pair of eyespots. The breeding of animals at Woods Holl during the months of June July and August. A preliminary account of the cleavage of Arenicola cristata, with remarks on the mosaic theory.