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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