Busycon carica is rare at Woods Hole, Mass.; B. canaliculatum can often be purchased from lobstermen in the vicinity. The egg-strings of B. canaliculatum (which have a single-keeled edge, according to Johnson, 1903) are sometimes found cast up on beaches in the Woods Hole-Falmouth area, but they are not very common.

Conklin (1907) states that the breeding season of B. canaliculatum occurs in late August and early September. The season for B. carica is apparently earlier; at Beaufort, N. C., the animals deposit their egg-strings in May and June.

PROCURING GAMETES:

The eggs and larvae do not live very long when brought into the laboratory, and the eggs are unsuitable for experimental purposes because they flatten out when they are removed from the protective jelly.

A. Egg Characteristics: The eggs of both species are laid in parchment-like, disc-shaped capsules attached to a long central cord; in both forms, the first few capsules of a cord may be small and empty. Within each of the subsequent capsules there are 10-20 eggs, embedded in a gelatinous matrix. The eggs of both species are very large and yolky; the average diameter of the egg of B. carica is approximately 1700 microns, while that of B. canaliculatum is about 1000 microns. There is no fertilization membrane present on either egg.

B. Cleavage and Gastrulation: The development of B. carica has been studied by Conklin (1907) and by McMurrich (1886, 1896); presumably, that of B. canaliculatum is similar. The following description applies to B. carica. Cleavage is spiral and almost equal, closely resembling that of Crepidula until the 56- to 60-cell stage. Small yolk lobes are formed during the first two cleavages; the micromeres are small and yolk-free. Cleavage in Busycon shows a transition between the holoblastic and meroblastic types. The mitotic figures of at least the first few divisions are very small, in relation to the size of the cells.

C. Rate of Development: In B. carica this is known to be slow; a period of about 13 months is apparently spent within the capsules.

D. Later Stages of Development: Due to the enormous supply of yolk, the closure of the blastopore occurs very slowly, and the larval organs appear on the upper surface of the yolk mass long before closure is completed. Shell gland, mantle, ganglia and velum are well formed before the blastopore closes. The foot, intestine, gills, larval kidney and heart appear during later development. For details and diagrams, see the papers of McMurrich (1886) and Conklin (1907).

CONKLIN, E. G., 1907. The embryology of Fulgar: A study of the influence of yolk on development. Proc. Acad. Nat. Sci, Philadelphia, 59: 320-359.

CONKLIN E. G., 1912. Cell size and nuclear size. J. Exp. Zool., 12: 1-98.

JOHNSON C. W., 1903. Some notes on the genus Fulgur. The Nautilus, 17: 73-75.

MCMURRICH, J. P., 1886. A contribution to the embryology of the prosobranch gasteropods. Stud. Biol. Lab., Johns Hopkins Univ., 3: 403 450.

McMurrich, J. P., 1896. The yolk-lobe and the centrosome of Fulgar carica. Anat. Anz 12: 534-539