Fig. 7. Effect on heart rate (fH) of a bolus injection of acetylcholine (100 µg kg^–1; time of injection indicated by dotted line) before (solid symbols) and after (open symbols) treatment with atropine (3 mg kg^–1) at 70% (A; N=4) and 90% (B; N=5) of development. Data are means ± S.E.M.