The burrows of these animals are exposed at low tide on the mud flats at Lagoon Pond and Hadley Harbor, near Woods Hole, Mass. The sexes are separate, the mature males being creamy white, the females pinkish-brown.

The latter part of June, and July (Bumpus, 1898). There is a definite periodicity, associated with the neap tides (Okada, 1941).

A. Care of Adults: Several males and females should be kept together in an aquarium containing a layer of sand brought in from their natural habitat. A tank 60 cm. long, 55 cm. wide and 75 cm. high is recommended by Okada (1941); the sand layer should be about 20 cm. deep. A constant stream of sea water running through this aquarium keeps the water level at about 50 cm.

B. Procuring Gametes: The jellied egg-masses can be collected at the mouths of the burrows where they are deposited at nightfall. Okada (1941) has been successful in inducing these animals to shed eggs in laboratory aquaria.

A. The Unfertilized Ovum: The egg is spheroidal in shape. In the Japanese form, the polar axis measures approximately 120 microns, while the diameter in polar view is 150 microns ( Okada, 1941). The egg is faintly pink in color, granular and almost opaque. It is homolecithal. Germinal vesicle breakdown occurs immediately after discharge into sea water (Okada, 1941). The eggs are embedded in large, irregular jelly-masses.

B. Fertilization and Cleavage: Fertilization occurs at the metaphase of the first polar division, and is followed by the lifting of a thick fertilization membrane and the formation of the first and second polar bodies (Okada, 1941). Cleavage is unequal and spiral, and the micromeres are relatively large. No polar lobes are formed. Gastrulation is by a combination of invagination and epiboly.

C. Rate of Development: The following time table of development at 23 to 25ûC. is given by Okada (1941). Time is calculated from shedding of the eggs.

Stage First cleavage Second cleavage Third cleavage Early blastula Gastrula	Time 7 hours 7-1/2 hours 8 hours 15 hours 24 hours
Stage Young trochophore Trunk segmentation, loss of capsule Three to five pairs of setae (embryos hatching from jelly-mass)	Time 2 days 3 days 4 days

D. Later Stages of Development: A trochophore is developed during late gastrulation. The free-swimming larvae within the jelly-mass are oval organisms, with a narrow prototroch and telotroch; a small ventral neurotroch and a posterior tuft of cilia are also present. At this time, there is a single pair of eyespots in the pre-trochal region. The hatched larvae have three to five pairs of setigerous segments and an additional pair of eyespots. Diagrams of the larvae can be found in the papers by Wilson (1882), Child (1900) and Okada (1941).

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

CHILD, C. M., 1897. A preliminary account of the cleavage of Arenicola cristata, with remarks on the mosaic theory. Zool. Bull., 1: 71-94.

CHILD, C. M., 1898. The maturation and fertilization of the egg of Arenicola marina. Trans. N. Y. Acad. Sci., 16: 387-394.

CHILD, C. M., 1900. The early development of Arenicola and Sternaspis. Arch. f. Entw., 9: 587-723.

DOWNING, E. R., 1911. The formation of the spermatophore in Arenicola and a theory of the alternation of generations in animals. J. Morph., 22: 1001-1051.

NEWELL, G. E., 1948. A contribution to our knowledge of the life history of Arenicola marina L. J. Mar. Biol. Assoc., 27: 554-580.

OKADA, K., 1941. The gametogenesis, the breeding habits, and the early development of Arenicola cristata Stimpson, a tubicolous polychaete. Sci. Rep. Tohoku Imp. Univ., ser. 4, Biol., 16: 99-146.

OKUDA, S., 1938. Notes on the spawning habit of Arenicola claparedii Levinsen. Annot. Zool. Japon., 17: 577-580.

WILSON, E. B., 1882. Observations on the early developmental stages of some polychaetous Annelides. Stud. Biol. [ab., Johns Hopkins Univ., 2: 271-299.