Fig. 1. Percent metamorphosis of Holopneustes purpurascens larvae (mean ± s.e.m.) of different ages after continuous exposure to 10 nmol l^–1, 100 nmol l^–1 and 1 µmol l^–1 dissolved histamine and SSW for 1 h (A), 24 h (B) and 72 h (C). Data from 7-day-old, 14-day-old and 21-day-old larvae were pooled from three batches (N=150 larvae per treatment); however, data shown for 28-day-old larvae are from batch A only (N=25 larvae per treatment).