Fig. 4. Observation of the cardiac tube in wild-type embryos. A schematic drawing of the cardiac cells in the cardiac tube is presented for each photograph. Double-headed arrows delineate the internal limit of the cardiac tube, small arrows show the ostiae cells and large arrowheads, the hemocytes. (A-H) Progression of the development of the aorta (A,B,E,F) and of the heart (C,D,G,H). The cardiomyocytes enlarge with the maturation of the cardiac tube. Ostiae are fully functional at 22 hours. (I-L) Recordings of heart beat at 22 hours allow measurement of the end-diastolic (d_d) and end-systolic (d_s) diameters. (M-V) Entry of hemolymph through the ostiae into the cardiac cavity is apparent from the passage of a large hemocyte (large arrowhead). The ostiae cells and the hemocytes adjust their shapes to allow transport of the hemocytes. Note the filamentous material (dotted lines) linking the two pairs of ostiae on either side of the cardiac tube.

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