This species grows in the form of upright, white, bushy tufts, 8 to 25 mm. high. The tube-like zooecia are arranged in two alternate rows. There is some question as to whether the species is dioecious or monoecious and protandrous. The conspicuous ovicells make the fertile "female" colonies easy to recognize. The form is common at Woods Hole, Mass.

In San Francisco Bay, the animals breed from late February to May. The limits of the breeding season have not been investigated in the Woods Hole region, although Rogick and Croasdale (1949) report that they found embryos in the ovicells as late as August 8.

A. Care of Adults: The colonies may be kept in aquaria supplied with an adequate amount of running sea water.

B. Methods of Observation: Although the animals must be sectioned if early developmental stages are desired, both the primary embryo and the secondary embryos can be dissected from the ovicells with fine needles.

A. Early Stages of Development: The early development of the eggs occurs in ovicells, which are highly modified zooecia. These structures are usually the modified second or third zooecium of an internode, although they are not present in each internode. The ovicell is a vase-like structure, consisting of a narrow stalk, a bulging mid-region and a short neck. The neck contains an opening through which the free-swimming larvae are released. The opacity of the ovicells, and the minute size of the eggs and developing embryos, make it impracticable to study early development by methods other than histological.

The eggs, measuring 18 microns or less in diameter, become associated with young zoid buds which are transformed into gonozoids. Only one egg develops in each gonozoid. Fertilization is internal, but the details of maturation and fertilization are not known. The early cleavages are unusual, in that the small follicle cells, which apparently serve as food for the developing embryo, actually penetrate between the blastomeres and separate them completely. The follicle cells start to disappear in the 24-cell stage and by the 60- or 70-cell stage, the embryo consists of a solid ball of cells, measuring about 43 microns in diameter. The increase in cell number continues until the embryo contains about 200 cells.

B. Later Stages of Development: When the primary embryo reaches the 200 cell stage, it sends out processes which bud off as secondary embryos. When they are first formed, these secondary embryos are solid balls of cells, measuring between 25 and 35 microns in diameter. They develop into very degenerate free-swimming larvae, which leave the gonozoids through the open mouth. The larvae of Crisia eburnea have apparently not been described, but if they resemble those of C. ramosa, they are simple, ciliated, sac-like structures, consisting of an inner and an outer layer of cells. One surface bears a large invagination or sucker, by which attachment is effected; the opposite pole, which develops into the mouth cavity of the primary zoid, is flattened and non-ciliated. For a further description and figures of the larvae, see the papers of Barrois (1877) and Harmer (1893).

BARROIS, J., 1877. Recherches sur l'embryologie des Bryozoaires. Travaux de l'Inst. Zool. de Lille et de la Station Maritime de Wimereux. Monograph.

BOBG, F., 1926. Studies on recent cyclostomatous Bryozoa. Zool. Bidrag Fran Uppsala, 10: 181-504.

HARMER, S. F., 1893. On the occurrence of embryonic fission in cyclostomatous Polyzoa. Quart. J. Micr. Sci., 34: 199-241.

ROBERTSON, A., 1903. Embryology and embryonic fission in the genus Crisia. Univ. Calif. Pub. Zool., 1: 115-156.

ROGICK, M. D., AND H. CROASDALE, 1949. Studies on marine bryozoa, III. Woods Hole region bryozoa associated with algae. Biol. Bull., 96: 32-69.

SIT-EN, L., 1944. The anatomy of Labiostomella Gisleni . . . with special regard to the embryo chambers of the different groups of Bryozoa and to the origin and development of the bryozoan zoarium. Kungl. Svensak Vetensk.. Handlingar, Tredje ser., 21: no. 6, pp. 3-111.