THE MECHANISM FOR SYNCHRONOUS SPAWNING IN HYDRACTINIA AND PENNARIA

¹ From the Zoology Department, Dartmouth College, and the Marine Biological Laboratory, Woods Hole

1. Methods are reported for scheduling the shedding of eggs and sperm by Hydractinia and Pennaria at any desired time of day.

2. Maturation in these animals occurs only after the germ cells have undergone a period of preparation in the darkness, and is initiated by direct action of light on the germ cells. Once initiated by light, maturation can proceed in the dark. Uninterrupted light, or uninterrupted darkness, results in complete cessation of maturation and spawning.

3. In Hydractinia maximum shedding requires at least an hour's darkness-preparation, although less time is sufficient for some eggs. Ten seconds of illumination is sufficient for widespread but not maximum initiation of maturation.

4. The hypothesis is advanced that darkness allows the accumulation of light-sensitive substances within the germ cell, whose breakdown initiates the process of maturation. Oöcytes dissected free from the organism can be matured by appropriate dark-light treatment.

5. Shedding of eggs and sperm takes place simultaneously with the completion of the maturation process. The swelling of jelly around the egg is not an important factor in bringing about shedding. Evidence is presented that contraction of the gonophore wall is an important factor.

6. Paralysis of the gonophore's musculo-epithelium by calcium-free sea water inhibits the shedding of mature eggs and sperm. Fertilization and cleavage of eggs within the gonophore have been produced in Hydractinia by causing maturation, inhibiting shedding and adding sperm.

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