The trophosome of B. superciliaris is about two inches tall, irregularly branched and light green in color. The pale rose hydranths have 15-20 tentacles in a single whorl about an inconspicuous hypostome. B. carolinensis is usually three to six inches tall; it is by far the commoner species at Woods Hole, Mass. The colony is light brown in color, with a greenish tinge; the red hydranths bear about 12 stiff, filiform tentacles on a long, flexible eversible proboscis. Both species- are found attached to Fucus and floating timbers, and B. carolinensis has also been collected from the dock of the U. S. Fish Commission. See the paper by Nutting (1901) for details and diagrams.

June, July and August. The medusae are reported to be present in August; the hydroids are available all summer, although some years they are difficult to find in June.

A. Care of Adults: The hydroid colonies should be kept in large dishes, supplied with running sea water. They should not be crowded.

B. Methods of Observation: Medusa development can be studied by clipping off the gonophores and mounting them on slides under a coverslip. Withdrawing a little of the water from under the coverslip (by absorbing it with a piece of lens paper) will exert a slight pressure on the gonophores and will bring out the structural details of the buds. The mature medusa buds can be dissected from the gonophores for study.

NORMAL DEVELOPMENT

A. Asexual Reproduction: The gonophores are borne singly or in clusters on the main stem and branches; they have the appearance of stalked sacs, and a single medusa is produced within each. The buds are scattered irregularly throughout the colony and there is no orderly arrangement as to age. The medusae develop within the gonophores until all the organs except the gonads are fully formed; then they break away and take up a free-swimming existence. Details concerning formation of the medusae are to be found in the papers by Goette (1907) and Hyman (1940).

The medusae of both species are similar, being sub-globular in shape and possessing four radial canals and a velum. The tentacles are in four groups, each group having a conspicuous eyespot at its base. The brick-red manubrium of B. carolinensis is shorter and more slender than that of B. superciliaris, but both species have four branched mouth tentacles. The free-swimming life lasts one or two months, during which time the gonads develop along the manubrium.

B. Sexual Reproduction: In B. superciliaris the fertilized eggs are retained in folds on the manubrium until the planula stage. A series of cleavages leads to the formation of a single-layered coeloblastula, which is transformed to a solid mass by a multipolar migration of cells. For details of this process, see the paper by Gerd (1892).

BERRILL N. J., 1949. Growth and form in gymnoblastic hydroids. I. Polymorphic development in Bougainvillia and Aselomaris. J. Morph., 84: 1-30.

GERD, W., 1892. Zur Frage über die Keimblätterbildung bei den Hydromedusen. Zool. Anz., 15: 312-316.

GOETTE A., 1907. Vergleichende Entwicklungsgeschichte der Geschlechtsindividuen der Hydropolypen. Zeitschr. f. wiss. Zool., 87: 1-336.

HYMAN, L. H., 1940. The Invertebrates: Protozoa through Ctenophora McGraw-Hill Book Co., New York.

NUTTING C. C., 1901. The hydroids of the Woods Hole region. Bull. U. S. Fish Comm., 19: 325-386.