REPRODUCTION IN PHORONOPSIS VIRIDIS. THE ANNUAL CYCLE IN THE GONADS, MATURATION AND FERTILIZATION OF THE OVUM

¹ Department of Zoology, McGill University, Montreal, Canada

1. The seasonal changes in the gonad of Phoronopsis viridis are described and are seen to involve the proliferation after spawning of vasoperitoneal tissue which is subsequently reduced and largely replaced by developing reproductive tissue.

2. No significant difference between the body lengths of male and female animals was found in the group of 169 animals measured. There is thus no evidence for protandry on the basis of body length.

3. Spermatozoa were found in the nephridia of both male and female animals and in the body cavity of female animals from January to May. Ripe eggs in the body cavity, in which the female nucleus is arrested at first metaphase, also contain a male nucleus. Eggs still covered by the investing epithelium and in which the germinal vesicle is still intact do not contain a male nucleus.

4. Ph. viridis is considered to be probably dioecious. Spermatozoa are believed to enter the female through the nephridium and fertilization appears to take place in the body cavity of the female, following the breakdown of the germinal vesicle. The egg when spawned is already fertilized and the maturation divisions proceed as soon as it is shed into sea water.