Fig. 4. Differences of maximal light emissions (L_max) of A. filiformis arm segments after stimulation by tryptamine (10^–4 mol l^–1 and 10^–5 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^–4 mol l^–1 and 10⁵ mol l^–1 tryptamine, respectively, in normal artificial seawater. **P<0.01; N=8 stimulated aliquot parts for each concentration.