Figure 1 in Studies on spider respiration and circulation by Victor Willem

Figure 1. Sagittal view of Pholcus J, X 15. I, II, III, pylocardium of the heart; ap, posterior artery; Sp, lung sinus. - The arrows indicate the direction and the size (on a scale 25 times larger than that of the drawing itself!) of the displacements of some points of the middle region of the body. The three thin lines shown for the posterior half of the abdomen correspond to the vertical swing of the abdomen; the thick lines correspond to local deformations.