Abstract
1. A study of the adult population of Sagitta setosa J. Müller has been made in the waters off Plymouth by weekly collections with the 2-metre stramin ring-trawl hauled obliquely in the daylight.2. Measurements of samples and a study of the state of development of the gonads has shown that there were apparently at least six broods of S. setosa during the period September, 1930, to August, 1931, inclusive.3. The successive broods were apparently spawning in September and October, 1930, and February, April-May, June, and July-August, 1931.

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