The medusae were formerly abundant at Woods Hole, Mass., in August, but at the present time they are relatively rare. Adult medusae are low and bell-shaped, with four long, tapering marginal tentacles. Three rudimentary tentacles are also present in each quadrant. The four-lobed mouth is located at the apex of a long manubrium which is borne on a gelatinous peduncle. The manubrium is two or three times the height of the bell. The gonads are located along the mid-section of the four radial canals. (See the paper of Hargitt, 1904, for a diagram.)

This species breeds during the summer months at Beaufort, N. C., but the breeding season at Woods Hole has not been determined.

A. Care of Adults: An adequate supply of fresh sea water is important.

B. Methods of Observation: Fertilized eggs can be obtained by placing several ripe animals in a small aquarium or battery jar of sea water. Shedding usually occurs between 7:30 and 8:30 P.M. on the night when the animals are collected.

Normal DEVELOPMENT

A. The Unfertilized Ovum: The eggs are said to be very clear and transparent, so that it is possible to observe details of development quite completely.

B. Cleavage and Gastrulation: 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.

C. Time Table of Development: Details of the developmental time sequence are not available, although development is rapid. Eggs shed at 8 P.M. develop into rapidly swimming planulae by the next morning.

D. Later Stages of Development and Metamorphosis: About 12 hours after fertilization, a ciliated, elongate planula is formed. 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. This invagination is gradually pushed toward one side of the larva (termed the "ventral" side) by the enlargement of one of the lips of the invagination. At the time of attachment, the invaginated "ventral" sac is everted and the glandular cells which cover it secrete an adhesive cement. The free end of the attached "root" then increases in length and the first hydranth develops at its apex. Subsequent hydranths are produced in a regular order behind this first individual.

The hydroid colonies are inconspicuous. The hydroids have a prominent round manubrium surrounded by a single circle of ten tentacles. The elongate, cylindrical hydranth body is not covered by the perisarc, and the stem lacks annulations.

BROOKS, W. K., 1886. The life-history of the Hydromedusae. Mem. Boston Soc. Nat. Hist. 3: 359-430.

HARGITT C. W., 1904. The medusae of the Woods Hole region. Bull. Burl Fish., 24: 21-79.