The gonads are located along the mid-section of the four radial canals. This species breeds during the summer months at Beaufort, N. C., but the breeding season at Woods Hole has not been determined. An adequate supply of fresh sea water is important. Fertilized eggs can be obtained by placing several ripe animals in a small aquarium or battery jar of sea water. The eggs are said to be very clear and transparent, so that it is possible to observe details of development quite completely.
Fertilization is apparently external.
Segmentation is total but not entirely regular, leading to the formation of a hollow, ciliated, one-layered blastula. The endoderm layer first appears at the posterior pole, but it is not clear as to whether this is a process of delamination or of cellular migration. Eggs shed at 8 P.M. develop into rapidly swimming planulae by the next morning. The cleavage cavity is reduced in the larva, but is still visible between the endoderm cells. The anterior end of the planula is the broader, and on the opposite end an invagination soon appears.