The colony consists of an erect, irregularly branching stem about one-half to three-fourths of an inch high. The hydrothecae are bell-shaped and have a toothed margin. The hydroids possess a single whorl of filiform tentacles. Gonothyrea is not common at Woods Hole, Mass.

A. Care of Adults: The colonies should be provided with an adequate supply of fresh sea water.

B. Methods of Observation: The eggs and larvae are difficult to dissect from the gonophores, and can best be studied by mounting whole gonophores on slides. Free-swimming planulae will readily attach and metamorphose in the laboratory if they are placed in covered Syracuse dishes of sea water.

A. Asexual Reproduction: The gonangia, which are borne in the axils of the branches, consist of a central blastostyle surrounded by a long, oval gonotheca. The gonophores, which are actually degenerate medusae, do not break away from the blastostyle but remain attached to it by means of short stalks, projecting outside the gonotheca in groups of three or four. In the development of the gonophores of both sexes, there are traces of radial and ring canals, and stubby tentacles are present on the distal ends of the sporosacs.

B. Sexual Reproduction: The eggs, of which there may be one or more present in each gonophore, are comparatively small (102 microns, according to Hargitt, 1919). They are fertilized in situ before maturation by sperm which are released by the male gonophores. Cleavage may be either regular or irregular. If it is regular, a coeloblastula is formed and the endoderm is formed by multipolar migration; if it is irregular, a solid morula is formed and both ectoderm and endoderm differentiate directly from this. In either type of development the resulting planula is a solid, oval mass of cells. This soon elongates, becomes ciliated, and develops traces of a coelenteron. At this time it escapes from the gonophore.

C. Later Stages of Development and Metamorphosis: The planula, which shows a well-developed coelenteron, swims about for 6-12 hours and then attaches by its broader, anterior pole. At the time of attachment, it loses its cilia and flattens out. The widened base soon begins to secrete a perisarc. Following these events, there is an elongation perpendicular to the attachment, and the development of a mouth and tentacles at the free end. Details of gonophore formation are available in the paper by Goette (1907) and the entire development, through metamorphosis, is described by Wulfert (1902).

BERRILL, N. J., 1950. Growth and form in calyptoblastic hydroids. II. Polymorphism within the Campanularidae. J. Morph., 87: 1-26.

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

HARGITT, G. T., 1919. Germ cells of coelenterates. VI. General considerations, discussion, conclusions. J. Morph., 33: 1-58.

WULFERT, J., 1902. Die Embryonalentwicklung von Gonothyraea loveni Allm. Zeitschr. f. wiss. Zool., 71: 296 327.