Fig. 4. Filling of the hearts by segmental afferent vessels. (A) Scanning electron micrograph of heart segments 15 and 16 in a corrosion cast in the intestinal region. Left and right latero-dorsal vessels fuse (fusion area; small asterisk) above the dorsal intestinal vessel (1) and form the latero-dorsal arches (asterisks). The dotted line follows the left latero-dorsal arch of segment 15 from its fusion point with the right arch to its valve at the heart. In comparison, the latero-lateral vessel (llv) is smaller and shorter. Its insertion point into the hearts is seen in two locations where the vessel broke away (arrows). Note the ventral vessel (2) with the enlargement for the ganglion of segment 15. Most capillary beds (integument, muscles, testes, nephridia) were removed. Scale bar, 1 mm. (B) Optical recordings from the latero-dorsal arch and the heart in the left hemisegment 15 (synchronous mode). In this preparation, the latero-dorsal arch constricted before the heart with an average phase difference of –23±3% (14 consecutive beats). (C) A single cardiac cycle (shaded area in B) is enlarged and shows the time points of the consecutive images of D. (D) Ventral aspect of segments 12–15 in the same animal as in B showing both hearts (arrows) and the latero-dorsal arches (asterisks). Analysis windows were drawn around the left heart of segment 15 and the latero-dorsal arch for optical recordings (rectangle in a). Consecutive images (a–d) show the timing of the constrictions of the latero-dorsal arch (dots) and the heart for the cardiac cycle enlarged in C. (a) Latero-dorsal arch filled, heart partially filled; (b) constriction of the latero-dorsal arch (no dots) fills the heart to maximal diastole; (c) heart in systole; latero-dorsal arch fills; (d) heart empty; latero-dorsal arch filled. Optical recordings are from intact juvenile leeches. Anterior is to the top.