The sand crab, Emerita, is common on sandy beaches; the animals migrate, with the tide, up or down the beach. The females are about twice the size of the males; according to MacGinitie (1938), the males outnumber the females by a ratio of three to one during the early part of the breeding season.

On the California coast, in May and June the season is at its height. -However, females with eggs in young stages have been found as late as October. Females carry their eggs for a period of four to five months. It appears that in general, mating of the California forms takes place in the late spring or early summer, although females with eggs are found throughout the year.

The breeding season for this form in the Woods Hole, Mass., region has not been accurately determined, although females with eggs have been found in July and August (Bumpus, 1898).

A. Care of Adults: Animals may be kept in large fingerbowls which are three-fourths filled with sand. An abundant supply of running sea water, led in under the sand, should be provided. Molted exuviae occasionally appear on top of the sand layer; these should be removed promptly.

B. Procuring Gametes and Embryos: For details concerning the mating habits of Emerita, see the paper by MacGinitie (1938). The time of mating can be detected by observing the behavior of the animals; several males will gather around a female for as many as five days in advance of egg-laying. Sperm will be deposited in ribbons of mucus on the ventral side of the female; shortly afterward, the female begins the egg-laying process. Eggs are deposited under the telson, on the ventral surface of the abdomen; the process may occur over a period of three days. Diagrams of the male reproductive system of Hippa pacifica are presented by Matthews (1956).

C. Methods of Observation: Embryos may be removed from the egg-mass at any time, by holding the female gently, prying up the telson, and removing a few embryos with forceps.

Cleavage stages are more clearly observed if the embryos are first treated with 1% chromic acid, washed in water and mounted under mica coverslips. Older stages are more difficult to study satisfactorily; they should be killed, to whiten the embryonic area, using mercuric chloride. The embryonic regions begin to whiten in a few minutes; strong aceto-carmine (with a little sea water) should then be used. After a few minutes, put the eggs in 50 % glycerine, which causes the stain to fade.

A. The Unfertilized Ovum: The eggs are orange to scarlet in color, and measure approximately 380 microns in diameter. They are attached to the egg-mass by thin stalks, and remain on the ventral surface of the female until the zoeae hatch; presumably, the eggs do not develop further if they are detached from the egg-mass.

B. Cleavage and Gastrulation: Divisions appear to be total, but there is some question as to whether the cleavage furrows actually penetrate the yolk mass. Cleavage stages are more frequently found in Emerita eggs than in Libinia eggs.

Gastrulation is similar to that in Libinia, and there is a corresponding development of the embryonic rudiments in the embryonic area. Fixation of the cells with mercuric chloride (as noted above) and study by reflected light will facilitate observations.

C. Later Stages of Development: The zoea larvae hatch from the egg membranes and may be kept in fingerbowls supplied with pieces of Ulva; the larvae should be fed diatoms.

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

MACGINITIE, G. E., 1938. Movements and mating habits of the sand crab, Emerita analoga. Amer. Midl. Nat., 19: 471-481.

MATTHEWS, D. C., 1956. The origin of the spermatophoric mass of the sand crab, Hippa pacifica. Quart. J. Micr. Sci., 97: 257-268.