Fig. 2. Assessment of total vessel capacity in corrosion casts (A,B) and dissected animals (C,D). (A) Scanning electron micrograph of a transverse section through a corrosion cast near the segmental border of segments 4 and 5 to show the different vascular beds used to assess total vessel capacity: hearts; afferent latero-dorsal vessels (asterisks); ventral vessel (1; with the imprint of the connectives between the segmental ganglia); dorsal vessel (2); capillary beds of the integument and the muscular envelope and capillary beds of the inner organs (polygons). Note the small-caliber capillaries of the integument and the somewhat larger capillaries of the adjacent layer in the body wall musculature. Scale bar, 1 mm. (B) Blood vessel capacity was assessed by dissecting and weighing the vascular beds of completely filled corrosion casts. The graph shows the average of two casts. About 60% of the total blood volume is stored in the capillary beds of the inner organs and the body wall and its musculature. (C) Segment length and the end-diastolic diameter of individual heart segments vary along the body axis. Segment length was measured in eight intact leeches (grey squares). The diameter of individual heart segments (blue triangles) and of the dorsal vessel in segment 10 (blue filled circle) were measured in one cast. The end-diastolic diameters of the hearts (red diamonds; number of measurements in italics), the afferent vessels (green circles; ldv, latero-dorsal vessel; llv, latero-lateral vessel), the latero-abdominal vessel (purple circle, lav) as well as the diameter of the dorsal vessel (grey circle) were measured in freshly dissected leeches. Values are plotted as a percentage of segment 10 (means ± s.d.). Absolute values for segment 10 are given on the graph. (D) Using segment length and the end-diastolic diameter, the end-diastolic volume was calculated for each heart segment assuming a straight cylinder. All data from adult leeches.