Fig. 1. Red-phase and green-phase male Carcinus maenas differ in the occurrence of methyl farnesoate (MF) in their hemolymph and in their testicular development. (A) Red-phase males (N=37) are more likely to have detectable MF (>2 ng ml^–1) in their hemolymph than green-phase animals (N=24; ^**P<0.01; Fisher's exact test). (B) The testicular index (TI) was 79% greater in red-phase than in green-phase crabs (values ± s.e.m.; N=12 for each group; ^***P<0.001; Student's t-test).