( POLYCHAETA )

Sthenelais leidyi

The adults are rather flattened, elongate worms, covered with flat scales which alternate anteriorly with dorsal cirri. The body color is grey, with a mid-dorsal stripe; the head is brown with a central red spot, two pairs of eyes, and a single tentacle. The worms have been collected at Hadley Harbor, near Woods Hole, Mass., but are not abundant. They can be obtained by sand-sieving.

The limits of the season have not been determined; however, mature animals have been obtained during the middle and latter parts of August (Bumpus, 1898).

A. Care of Adults: The worms should be isolated in fingerbowls of sea water when brought into the laboratory.

B. Procuring Gametes: Mature animals usually shed a few hours after collection. Body-cavity eggs, obtained by cutting up a female, do not develop as well as those which are spawned normally. The males and females should be removed from their respective dishes as soon as shedding is completed.

C. Preparation of Cultures: Only one or two drops of dilute sperm suspension should be added to a fingerbowl of eggs; over-insemination results in abnormal cleavage. The embryos may be raised through the trochophore stage. Swimming larvae should be decanted to bowls of fresh sea water daily.

A. The Unfertilized Ovum: The egg is approximately 110 microns in diameter, very opaque, and flattened and triangular in shape when shed. It has not been ascertained whether the germinal vesicle breaks down before shedding, or whether this occurs soon after contact with sea water.

B. Fertilization and Cleavage: The eggs in which germinal vesicle breakdown has occurred can be fertilized. As soon as fertilization occurs, a wrinkled fertilization membrane rises from the egg surface. Cleavage is spiral and almost equal; gastrulation is probably by invagination.

C. Time Table of Development: The following schedule indicates the development of an egg batch at a temperature of 23û to 24û C. Times are given from insemination.

Stage Polar bodies formed First cleavage Second cleavage Third cleavage Free-swimming embryos Trochophores

Time 30 minutes 40-45 minutes 6.0 minutes 85 minutes 3-1/2 hours 17 hours

D. Later Stages of Development: The larva is a large, plump trochophore which swims with a peculiar end-over-end motion. When fully formed, it has a long, stiff, apical tuft, and a telotroch. In addition, a long tuft of cilia projects from the lower left corner of the mouth. A pair of eyespots and prototrochial pigment appear during development. The stomach is very large and vesicular; the intestine and oesophagus are small.

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