Razor clams are found burrowing in muddy sand habitats, which are also suitable for collecting Mya. They are procured by rapid digging at low tide. One of the best collecting grounds in the Woods Hole region is Barnstable Harbor, Mass., and another is Rand's Harbor, Mass. The sexes are separate, but cannot be distinguished externally.

Little is known of the breeding season of this species, but according to Just (1939), mature animals are found at Woods Hole during July. It is probable that spawning begins before this, since in the colder waters at Prince Edward Island, larvae have been found in the plankton throughout June (Sullivan, 1948).

A. Care of Adults: In the laboratory, the animals should be kept in wet sand in an aquarium, protected from increases in temperature.

B. Procuring Gametes: Fertilization is internal, but it is possible to obtain fully mature, unfertilized eggs. Best results are obtained with adults over five inches long. Such animals isolated in large fingerbowls will, according to Just (1939), shed naturally. Gametes may also be obtained directly from the gonads. To do this, remove one valve, exposing the gonads (white irregular masses) which lie on and around the dark brown digestive gland, just anterior to the heart. Remove the gonads with forceps or a pipette, and isolate in a watch glass. The gametes will ooze out, and when this extrusion has ceased, the gonads should be removed. The eggs are relatively clean, and require little washing. They remain fertilizable for five hours, but with a decreasing percentage of fertilization.

C. Preparation of Cultures: If fertilization has already taken place, eggs may be found in various stages of development. Unfertilized eggs may be inseminated by adding several pipettes-fur of sperm suspension. After a short time, change the sea water, in order to remove excess sperm. The cultures should be kept in a large amount of water and stored on a water table. The sea water in the cultures should be changed at least once a day. Loosanoff (1954) describes a method for culturing older larvae of this form.

A. The Unfertilized Ovum: The egg of Ensis may be quite irregular in shape; it is enclosed in a thin vitelline membrane and surrounded by a narrow perivitelline space. The ovum is light yellowish-brown in color. It is rather granular, but moderately transparent, and has a large germinal vesicle.

B. The Spermatozoon: The sperm are green in color, and relatively large, the head measuring 2.8 microns in width and 5.6 microns in length. They have a very long tail.

C. Fertilization and Cleavage: Shortly after insemination, the egg rounds up and the germinal vesicle breaks down. The egg now measures 65 to 67 microns in diameter. Two polar bodies are given off, and prominent polar lobes are formed prior to each of the first two cleavages. Since the eggs are relatively transparent, the phases of spindle formation in cell division are readily distinguished. Cleavage is unequal and spiral. A ciliated blastula is formed, which hatches and swims in a clockwise circular manner at the surface. Gastrulation is by epiboly and invagination.

D. Time Table of Development: The following schedule represents a range of times observed in cultures developing at laboratory temperatures ranging from 27 to 30û C. Times are recorded from insemination.

Stage Germinal vesicle breakdown First polar body Second polar body First polar lobe First cleavage Second polar lobe Second cleavage Third cleavage Morula Free-swimming blastula Gastrula Early trochophore Early veliger

Time 3 to 5 minutes 15 to 20 minutes 25 to 30 minutes 30 to 35 minutes 42 to 46 minutes 50 to 60 minutes 58 to 65 minutes 75 to 85 minutes 2-1/2 hours 3-3/4 to 4 hours 10 hours 11 hours 27 hours

E. Later Stages of Development The ciliated gastrula is bell-shaped, with a prominent flagellum. It transforms rapidly into a typical trochophore, oval in shape. At the end of one day, the shell gland can be seen and the early veliger soon develops. The shell increases in size and has a long straight hinge. By the end of the second day, many of the veligers have lost their flagella. The velums are reduced in size. The viscera appear as an amorphous, coarse, granulated mass. The larvae are pale yellow throughout their development, darkening only just before settling to the bottom. The larval life seems to be of relatively short duration (Sullivan, 1948).

JUST, E. E., 1939. Basic Methods for Experiments on Eggs of Marine Animals. P. Blakiston's Son and Co., Inc., Philadelphia, pp. 33-34.

LOOSANOFF, V. L., 1954. New advances in the study of bivalve larvae. Amer. Sci, 42: 607624.

SULLIVAN, C. M., 1948. Bivalve larvae of Malpeque Bay, P. E. I. Bull. Fish. Res. Bd., Canada, no. 77, PP. 1-36.