These are by far the smallest and their contribution to the total circulation is relatively minor. This will at the most involve impairment of the most anterior set of lateral hearts. The method of cannulation will of necessity obstruct flow anterior to the point of cannulation. The catheter was passed from 10 to 15 mm. The catheters used were of standardized length (30 cm.) made of 20- or 50-gauge polyethylene tubing and filled with earthworm Ringer. Two ligatures were passed under the vessel. By careful dissection with a blunt instrument the dorsal vessel was freed from adjoining tissue anterior to its bifurcation into the two lateral hearts of the segment. The incision followed the septum closely on its posterior side. dorsal to the setae on one side ending in the same point at the contra-lateral side.
incision was made extending transversely from about 10 mm. When cannulations were made for simultaneous recordings of pressures in the dorsal and ventral vessels an incision was first made dorsally in segment 8. Upon induction of suitable muscle relaxation an earthworm was transferred from the solution of propylene-phenoxytol to the operating table and placed on moist paper. These hearts provide the pumping power needed to set up the distributing flow of blood. These commissures contain the lateral hearts, often called pseudohearts. The vessel now gives rise to the five pairs of large commissures to the ventral vessel. In front of segment 12 the dorsal vessel ceases to be a collecting vessel. The dorsal vessel has an inherent rhythmic peristalsis in postero-anterior direction driving blood forwards. As the main collecting vessel it receives blood from the dorso-intestinal vessels and the dorso-subneural commissures. It is closely adherent to the gut except in the anterior region of the lateral hearts. It is found dorsal to the alimentary canal and traverses the entire length of the body. This vessel is the most conspicuous in the animal. In the earthworms the largest vessel, the dorsal vessel, constitutes the most important collecting vessel.
Apart from the central pumping mechanism auxiliary mechanisms for blood propulsion can be spaced throughout the vascular channels. All closed vascular systems are arranged in collecting and distributing vessels usually with a central focus or meeting site in a propulsive blood-pumping mechanism.
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