Ripe specimens of these brittle stars are usually not available at Woods Hole, Mass., but they may be dredged from the colder waters to the north. Bumpus (1898) received large numbers of them in good condition, shipped in artificially cooled containers from Nahant, Mass., to Woods Hole.

The sexes are separate. During the breeding season the gonads can be seen through the skin on the underside of the disc. The ovaries are yellowish-red and the testes white.

Fewkes (1886) stated that animals at Eastport, Maine, breed in summer until mid-August. At Nahant, in 1898, ripe animals were obtained from mid-May to the end of June (Bumpus, 1898).

A. Care of Adults: The adults may be stored in aquaria in a cool place. It is advisable to obtain fresh material quite often.

B. Procuring Gametes: Ripe animals will usually spawn about 15 to 30 minutes after they are placed in sea water at room temperature. The males usually, but not always, spawn first. Eggs may be obtained by removing the ovaries, cutting them in two, and allowing the eggs to roll out. Eggs which tend to cling together instead of rolling out are immature and should be discarded. The best way to obtain ripe eggs is to isolate a shedding female in a small container, first rinsing the animal in tap water. The eggs are shed within a short time, and it is probable that all which are ripe are released (Olsen, 1942).

C. Preparation of Cultures: The eggs should be transferred to a fingerbowl of fresh sea water, where they may be inseminated by adding a small amount of sperm suspension. All the eggs are fertilized, and should receive a change of sea water after a short time. They need little care until after hatching. Olsen (1942) gives methods for feeding the larvae with cultured phytoplankton.

D. Methods of Observation: The study of the developing skeleton of these embryos is greatly facilitated by the use of polarized light.

E. Removal of Membranes: The fertilization membrane can be removed with the aid of a pipette. This is most easily accomplished immediately after its formation. Development of the denuded egg proceeds normally.

NORMAL DEVELOPMENT

A. The Unfertilized Ovum: The mature egg is spherical in shape and measures approximately 105 microns in diameter (Olsen, 1942). It is surrounded by a gelatinous capsule, which disappears about 10 minutes after fertilization. Fewkes (1886) described the egg as faintly green in color; the Norwegian variety is reportedly reddish-yellow or yellowish-brown (Olsen, 1942). The ovum is shed after the breakdown of the germinal vesicle.

B. Fertilization and Cleavage: About one minute after fertilization, the fertilization membrane begins to elevate, leaving a small perivitelline space. The diameter across the fertilization membrane is approximately 130 microns. A transparent hyaline layer, consisting of two parts, can now be seen surrounding the yolky portion of the egg. The outer part, which is as clear as glass, remains on the egg surface throughout cleavage, while the inner, with dark radial stripes or shadows, sinks between the blastomeres during cleavage and surrounds them completely (Olsen, 1942). Soon after fertilization, the egg becomes irregular in shape, and remains thus until after the first cleavage. Meanwhile, two polar bodies are formed. They are retained for some time under the fertilization membrane, but not in any fixed position.

The cleavage pattern is usually irregular (Olsen, 1942). An ovoid, ciliated blastula is formed. It hatches and rotates slowly to the surface. Gastrulation is by invagination. The two portions of the hyaline layer can be followed through to late larval stages. For figures of cleavage and gastrulation, consult the papers by Fewkes (1886) and Olsen (1942).

C. Time Table of Development Olsen (1942) reared the Norwegian form of this species in sea water at 8û C., and recorded the following times from fertilization for the early stages of development:

Stage First cleavage Second cleavage Third cleavage Fourth cleavage Fifth cleavage Hatching (blastula) Gastrulation Young pluteus Full-grown pluteus

Time 3 hours 5 hours 5 hours, 45 minutes 6 hours, 30 minutes 7 hours, 30 minutes 24 hours 27 to 48 hours 3 to 4 days about 30 days

These times agree with the few observations of the New England species recorded by Fewkes (1886); however, it is unlikely that his animals were reared at such a low temperature&endash;none is indicated.

D. Later Stages of Development and Metamorphosis: The larval gastrula transforms into a young pluteus, with a calcareous skeleton and rudimentary arms. By the fourth day the alimentary tract and primitive coelom are formed, and the arms have increased in size. Older larvae (about 17 days) are characterized by the development of a fourth pair of ciliated arms, and the exceptional length of the postero-lateral pair. The developing hydrocoele may be seen after 20 days, and by 30 days the pluteus is full grown. Metamorphosis begins with the formation of the adult skeleton, and has been described in detail by Olsen (1942). Figures of these stages may be found in papers by Fewkes (1886, 1887) and Olsen (1942).

BUMPUS, H. C., 1898. The breeding of animals at Woods Holl during the months of June, July and August. Science, 8: 850-858.

FEWKES, J. W., 1886. Preliminary observations on the development of Ophiopholis and Echinarachnius. Bull. Mus. Comp. Zool., Harvard, 12: 105-152.

FEWKES, J. W., 1887. On the development of the calcareous plates of Amphiura. Bull. Mus. Comp. Zool., Harvard, 13: 107-150.

OLSEN, H., 1942. The development of the brittle-star Ophiopholis aculeata (O. Fr. Müller) with a short report on the outer hyaline layer. Bergens Mus. Arb., 1942, Naturv. Rekke Nr. 6, S. 1-107.