Fig. 6. Comparison of periodic heartbeat traces of first with third heart segment in D. hydei (male 4). (A) Sensor beside the waist at the transition of the first heart segment to the aorta. The mean IR-transmittance is decreasing during retrograde pulsations, when no hemolymph is pumped through the aorta. Pulses, probably of the intestine, with a lower frequency are superimposed on the heart pulses (arrows). (B) Same individual, with sensor beside the third heart segment the next day. Mean IR-transmittance is increasing during retrograde pulsations, when hemolymph is accumulating in the abdomen.