ON THE REPRODUCTIVE CYCLE AND BREEDING HABITS OF TWO WESTERN SPECIES OF HALIOTIS ,

1. The annual reproductive cycles were determined for two species of abalone: Haliotis cracherodii and H. rufescens, all found in Monterey Bay. The method consisted of tracing on transparent thin plastic the perimeter of the gonad and hepatic tissues. The tracings were cut and weighed. The areas of these tissues were determined from a standard curve which related the area of the plastic to its weight. The ratio of the area of the gonad (or hepatic tissue) to the shell length x 100 yields an index for measuring seasonal changes in the quantity of these tissues. 2. H. cracherodii shows a marked summer breeding season, the rapid and precipitous spawn-out being indicated by the decline in the size of the gonad. 3. H. rufescens shows an ill-defined breeding season and, from reports, seems to spawn at all times of the year. The gonad size was found to vary little during the year except for an increase in winter. 4. In both species the hepatic index is inversely correlated with the gonad index. 5. A summary of the breeding seasons reported in the literature for eight species of Haliotis from various parts of the world is discussed.