1. The scientific name of earthworm is megascolex. It consists of hearts, blood vessel and blood.
2. There are 8 pairs of hearts in the earthworm which are placed laterally inside the body. Blood vessels are closed tubes and are connected to hearts.
3. These hearts connect the two major blood vessels in the earthworm - a DORSAL BLOOD VESSEL and a VENTRAL BLOOD VESSEL. These are above and below the alimentary canal.
4. The dorsal blood vessel is a receiving blood vessel. It receives blood from various organs present in each segment of the body. So, it acts as a chief vein in the body.
5. The ventral blood vessel is a distributing vessel - it supplies blood to various organs present in each body segment. So, it acts as a chief artery in the body.
6. In the dorsal blood vessel, blood flows in posterior to anterior direction and in the ventral blood vessel it flows in anterior to posterior direction.

Blood flow is from Body parts → Dorsal Blood Vessel → Hearts → Ventral Blood Vessel→ Body parts.