The adult polyclads are found inhabiting the mantle cavity of Busycon canaliculatum and may easily be dissected from the gill chambers. They are numerous in freshly caught specimens of Busycon, but the worms rapidly decrease in number if the snails are allowed to remain in the aquaria for a few days.

If adult worms are placed in jars of fresh sea water through which an air current is allowed to bubble, they will soon deposit their eggs on the bottom or sides of the dish.

Surface (1907) warns that the eggs do not develop normally after experimental handling, although untreated eggs and larvae are easily reared in the laboratory.

A. Egg Characteristics: The eggs are deposited without any special orientation in tough, gelatinous, spiral capsules. Each capsule contains from 100 to 200 eggs, each of which is surrounded by a membrane. The eggs measure 100 microns in diameter and are densely granular with yolk. Fertilization is internal, although the eggs are still in the germinal vesicle stage when they are laid.

B. Cleavage and Gastrulation: Cleavage is unequal and spiral. It is peculiar in that, after giving off the fourth quartet of micromeres, the macromeres are very small and eventually degenerate. The fourth quartet of micromeres thus takes over the function of forming both endoderm and mesoderm. Gastrulation is by epiboly.

C. Time Table of Development: The first polar body is formed an hour after the eggs are laid; the second polar body and early cleavages follow- at one-hour intervals. Gastrulation is completed by the end of the second day; rotation within the capsules occurs on the third day; eyes appear on the fourth day; contractility and the development of ciliated lobes can be observed during the fifth day; and on the sixth day, the larvae leave the capsules.

D. Later Stages of Development : The larva is of the type known as Müller's larva. It is oval in shape, bearing at its lower pole an ectodermal stomodeum which leads to an irregular, ciliated, endodermal sac. Eight ciliated lobes can be seen just below the equator, and at the aboral pole a plate of very small cells covers a mass of ganglion cells. The further metamorphosis of the larva has not been followed in this species, although Lang (1884) has described the later development of a Müller's larva of another genus.

LANG, A., 1884. Die Polycladen (Seeplanarien) des Golfes von Neapel und der angrenzenden Meeresabschnitte. Fauna u. Flora d. Golfes von Neapel, 11: 1-688

MAcBRIDE, E. W., 1914. Text-Book of Embryology. Vol. I. Invertebrata. Macmillan and Co., Ltd., London, pp. 102-117.

SURFACE, F. M., 1907. The early development of a polyclad, Planocera inquilina Wh. Proc. Acad. Nat. Sci., Phila., 59: 514-559.