These worms live in U-shaped, rather tough, mud tubes. The adults are fairly easy to obtain, but ripe individuals are never abundant. The best collecting grounds are at Barnstable, Mass., although some animals are found in Hadley Harbor. They should be collected during the day at low tide, washed free of mud, and placed immediately in a bucket of sea water. The sexes are separate, and may be distinguished by the darker abdominal segments of the females.

June, July and August, the peak being in July. Lunar periodicity is marked, and ripe individuals are most plentiful within two days of the new or full moon (Scott, 1909).

A. Care of Adults: In the laboratory the worms should be washed and isolated in separate dishes. Injured worms tend to release their sexual products; for this reason, care should be taken to handle them gently, especially during transportation.

B. Procuring Gametes: Eggs obtained by cutting open the body wall can rarely be fertilized. However, if ripe, the worms will shed spontaneously during the afternoon or evening of the day of collection (Scott, 1909). The period of egglaying lasts 30 to 60 minutes, with large, immature eggs appearing toward the end of that time. The eggs remain fertilizable for as long as one hour after entering sea water.

C. Preparation of Cultures: Half an hour after insemination, the excess sperm should be washed off the eggs, and the cultures placed on a water table. When the larvae develop, they should be decanted daily to fresh sea water; from the fifth day on, those larvae which are metamorphosing should be kept in dishes with fresh Ulva (Mead, 1897).

A. The Unfertilized Ovum Under normal conditions the oocyte is retained in the body cavity until the metaphase of the first maturation division (Scott, 1906). When it is released from the ovary into the body cavity, the germinal vesicle breaks down and the egg, which until that time was spherical, flattens at the polar region. It measures 100 microns in diameter and is very opaque. A thin, wrinkled membrane is present (Mead, 1899), but it is slightly thicker than that of Lepidonotus (compare Figures 1 and 89 in the paper by Mead, 1897). There is a noticeable perivitelline space.

B. Cleavage: Cleavage is unequal and spiral. No polar lobes are formed. Gastrulation is by invagination (Mead, 1897).

C. Rate of Development: The rate of development is rapid. Swimming forms are present four to five hours after insemination, and well-formed trochophores in 20 hours. Larval segmentation starts at 36 hours, and metamorphosis begins at about the fifth day, when five trunk segments are present. By 11 days, metamorphosis is completed.

C. Later Stages of Development and Metamorphosis: The trochophore has a

wide prototroch, a neurotroch, and a paratroch. The frontal bodies and gland cells are prominent. Larval segmentation occurs early, and when the larvae have developed about five trunk segments, they cease to swim about freely, and, sinking to the bottom, begin to metamorphose. (See text figures 6, and 9-18, in the paper by Mead, 1897.)

JUST, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia.

MEAD, A. D., 1894. Preliminary account of the cell lineage of Amphitrite and other annelids. J Morph., 9: 465-473.

MEAD, A. D., 1897. The early development of marine annelids. J. Morph., 13: 227-326.

MEAD, A. D., 1899. The cell origin of the prototroch. Biol. Lectures M. B. L., Wood's Holl, Mass., 1898, pp. 113-138.

SCOTT, J. W., 1906. Morphology of the parthenogenetic development of Amphitrite. J. Exp. Zool., 3: 49-97.

SCOTT, J. W., 1909. Some egg-laying habits of Amphitrite ornata Verrill. Biol. Bull., 17: 327-340.

SCOTT, J. W., 1911. Further experiments on the methods of egg-laying in Amphitrite. Biol. Bull., 20: 252-265.

TREADWELL, A. L., 1898. The cell lineage of Podarke obscura. Preliminary communication. Zool. Bull., 1: 195-203.

TREADWELL, A. L., 1899. Equal and unequal cleavage in annelids. Biol. Lectures M. B. L., Wood's Holl, Mass., 1898, pp. 93-111.