Fig. 7. Long-term optical recordings were used to assess volume differences in the hearts with respect to coordination mode. Recordings are from heart segments 4, 6, 8 and 10 (A) and from heart segments 13–16 (B) on both sides (peristaltic mode, shaded boxes; synchronous mode, no shading). Small arrows denote emptying (A, left heart, segment 10; B, left heart segment 13). In the top panel, dotted lines ease visualization of the characteristic intersegmental phase differences in the two modes. We assessed the end-diastolic volume as the maximum amplitude of the optical signal and the pumped volume during one cardiac cycle as the area under the curve (shaded areas in A, left heart). Heart segments 4–10 carry less blood in the synchronous mode than in the peristaltic mode. (B) Two switches in coordination mode are shown for posterior heart segments to emphasize the regular timing of constrictions as well as the precipitous and reciprocal switches in these quiescent leeches (different animal from that in A). Note that the posterior heart segments constrict nearly simultaneously (see text and Fig. 6). The differences in pumped and end-diastolic blood volume were less obvious in segments 14–16. (C) Ratio of the total blood volume pumped (squares) and the end-diastolic volume (diamonds) in the synchronous vs the peristaltic coordination mode from four animals. A ratio of 1 (horizontal dotted line) indicates no volume difference between coordination modes. Values are means ± s.d., with the number of preparations for each segment given in parentheses.