The mature ovum is red-brown in color and is spherical, measuring 150 to 180 microns in diameter. It is enclosed in a chitinous, highly refractive vitelline membrane, which is three to four microns thick. The ovum is shed after formation of the first maturation spindle. Cleavage is unequal and spiral, producing a D cell that is perhaps five times as large as the A, Bor C cells. The micromeres of the first quartet are exceptionally large.
Gastrulation is by epiboly.
The temperature was not recorded. By 48 hours the digestive tract is well developed, two eyespots are present, and the pre-oral band of long cilia is conspicuous. At metamorphosis, the yolk membrane is cast off and the body elongates. Studies on the embryology of the Sipunculidae. The embryonal envelope and its homologue.