Fig. 4.

Larval and adult heart structure. All images are fluorescence micrographs of specimens treated with Alexa Fluor conjugated phalloidin, which labels muscles green. (A) Image of the larval dorsal thorax and abdomen showing that the dorsal vessel extends the length of the body along the dorsal midline and is subdivided into an abdominal heart (arrows) and a thoracic aorta (arrowheads). The dashed line delineates the thoraco-abdominal junction. (B) A portion of the larval abdomen illustrated in panel A, magnified to show the heart (arrows) and associated alary muscles (e.g. arrowheads). The larval heart is flanked on either side by large swim muscles that approach the heart at ~45 deg angles. (C) High magnification view of two segments of the larval heart (arrows) showing the spiral arrangement of cardiomyocytes, the dorsal longitudinal tracheal trunks (T) and the alary muscles (arrowheads). Also visible along the surface of the heart are numerous pericardial cells. (D) Adult dorsal abdomen showing the heart (arrows), which runs the length of the abdomen along the dorsal midline. (E) A portion of the adult abdomen magnified to show the heart (arrows) and the extensive alary muscles (arrowheads). All images are oriented with anterior on top. Scale bars: A and D, 500 μm; B and E, 200 μm; C, 100 μm.