This form is quite commonly found in the Woods Hole Mass., region; the shell is low and broad in form, with a smooth, yellow-white exterior. It usually occurs at or below the low-water mark, on stones, shells, timbers, etc. Burbanck et al. (1956) collected B. eburneus in abundance at Rand's Harbor, in areas of fresh water inflow.

Fish (1925) states that the breeding season of B. eburneus at Woods Hole extends from August to mid-November. At Beaufort, North Carolina, this barnacle apparently breeds from July to September (Costlow and Bookhout, personal communication).

A. Care of Adults: The animals should be kept in aquaria supplied with running sea water.

B. Procuring Embryos: Carefully chip away the calcareous portion of the basis. If the eggs are ripe and in the process of development, the egg lamellae are firm and, with care, may be removed intact. They should be placed in a fingerbowl of sea water; the eggs may be teased out with a needle.

C. Preparation of Cultures: The embryos and larvae are sensitive to temperature and oxygen changes. Therefore, the sea water in which they are kept should be changed frequently, and the cultures kept cool on a sea water table. Despite these precautions, the mortality rate is high. The addition of 200,000 to 400,000 units of penicillin per liter appears to reduce bacterial growth in the cultures (Costlow and Bookhout, 1957).

Aqueous extracts of mantle wall or body tissues, but not of egg-masses themselves, have been found to promote hatching and liberation of the nauplii (Crisp, 1956).

A. Fertilization and Cleavage: The available evidence indicates that barnacles normally are not self-fertile; however, Barnes and Crisp (1956) have collected some data which indicate that B. perf oratus eggs occasionally develop either parthenogenetically or as a consequence of self-fertilization.

Fertilization in B. eburneus is internal; in the youngest stages of development, it is possible to observe the formation of the polar bodies, and the approach of the germ nuclei. This is best seen in preparations which have dried somewhat, so

* Dr. J. D. Costlow, Jr. and Dr. C. G. Bookhout supplied much of the information on which this section is based; we should like to express our appreciation to them that the eggs are slightly flattened. Cleavage apparently is similar to that in the egg of Lepas, and gastrulation is by epiboly.

B. Time Table of Development: The over-all time for development of B. eburneus is quite short, as compared with that for many barnacles, and requires from 7 to 13 days (Costlow and Bookhout, 1957). At 26û C., the following durations for the naupliar and cyprid stages were recorded by Costlow and Bookhout (1957):

Stage First naupliar Second naupliar Third naupliar Fourth naupliar Fifth naupliar Sixth naupliar Cyprid

Time 15 minutes to 4 hours 1 to 2 days (average: 1 day) 1 to 4 days (average: 1.5 days) 1 to 4 days (average: 2 days) 1 to 5 days (average: 2.6 days) 2 to 4 days (average: 2.5 days) 1 to 14 days

C. Later Stages of Development A three- and a five-segment stage are undergone by B. eburneus (Costlow and Bookhout, personal communication). The organogeny of the developing embryo is complex; Groom (1894) gives diagrams of the early development and later phases of B. perforatus.

Free-swimming stages: Costlow and Bookhout (1957) describe the six naupliar and one cyprid stage of B. eburneus, giving setation formulae, specific morphological characteristics, frequency of molting, duration of intermolt periods, and time of complete development in the laboratory. The use of a motile source of food, such as Arbacia plutei and Chlamydomonas, is necessary in order to maintain the animals throughout the larval period.

Setting and metamorphosis: Costlow and Bookhout (1953, 1956) describe methods for collecting the cyprid stage of B. improvisus and B. amphitrite niveus. They use six-inch plastic squares, which are suspended in water known to be inhabited by the adults. Small squares of plastic, containing individual cyprids, may be cut from the larger collecting-square and observed, from either surface, under the microscope. Metamorphosis of the cyprid into the "pin-head" stage is described for B. amphitrite niveus by Doochin (1951). The subsequent development of the characteristic six mural plates of the adult barnacle is described for B. improvisus by Costlow (1956).

BARNES, H., AND D. J. CRISP, 1956. Evidence of self-fertilization in certain species of barnacles J. Mar. Biol. Assoc., 35: 631-639.

BURBANCX, W. D., M. E. PIERCE AND G. C. WHITELEY, JR., 1956. A study of the bottom fauna of Rand's Harbor, Massachusetts: An application of the ecotone concept. Ecol Monog., 26: 213-243.

COSTLOW, J. D., JR., 1956. Shell development in Balanus improvisus Darwin. J. Morph., 99 : 359-415.

COSTLOW, J. D., JR., AND C. G. BOOKHOUT, 1953. Moulting and growth in Balanus improvisus.. Biol. Bull., 105: 420-433.

COSTLOW, J. D., JR., AND C. G. BOOKHOUT, 1956. Molting and shell growth in Balanus amphitrite niveus. Biol. Bull., 110: 107-116.

COSTLOW, J. D., JR., AND C. G. BOOKHOUT, 1957.

Larval development of Balanus eburneus in the laboratory. Biol. Bull., 112: 313-324.

CRISP, D. J., 1956. A substance promoting hatching and liberation of young in Cirripedes. Nature, 178: 263.

DOOCHIN, H. D., 1951. The morphology of Balanus improvisus Darwin and Balanus amphitrite niveus Darwin during initial attachment and metamorphosis. Bull. Mar. Sci Gulf and Caribbean, 1: 15-39.

FISH, C. J., 1925. Seasonal distribution of the plankton of the Woods Hole region. Burl Fish., Document no. 975.

GROOM, T. T., 1894. On the early development of Cirripedia. Phil. Trans. Roy. Soc., London, ser. B, 185: 119-232.