Fig. 6. Differences of maximal light emissions (L_max) of A. filiformis arm segments after stimulation by octopamine (10^–9 mol l^–1 and 10^–10 mol l^–1) in normal ASW and in Ca²⁺-free ASW. Values (means ± S.E.M.) are expressed as a percentage of photogenesis triggered by 10^–9 mol l^–1 and 10^–10 mol l^–1 octopamine, respectively, in normal artificial seawater. **P<0.01; N=6 stimulated aliquot parts for each concentration.