1. The percentages of males and females in naturally occurring chains of Crepidula fornicata L. were found to be 39% females, 6% ‘transients’ and 55% males.
2. Disconnected males kept in cages in sea water for 9 months re-established the normal sex ratio.
3. Disconnected males were kept for periods of 4-6 weeks at temperatures of 30° and 10° C. No significant tendency to change sex was observed.
4. Males were injected with extracts of females. No tendency to change sex was observed.
5. In animals of all sizes from small males to large females both male and female gametes are invariably present together. The gametes of both sexes are polymorphic.