From the gizzard, food passes into the intetine, which extends posteriorly to the anus. Use a probe to feel the relative thicknesses of the walls of the crop and gizzard. Use your scalpel to make a cross-sectional cut through the intestine about half way along its length. Examine the cut end of the intestine with a hand lens or dissecting microscope. The earthworm has a closed circulatory system.
Blood is pumped through vessels by five pairs of aortic arches, or hearts.
The aortic arches encircle the esophagus between segments seven and eleven. From the aortic arches, blood flows into the ventral vessel, which runs beneath the organs of the digestive tract. The ventral vessel branches and divides into smaller vessels, eventually forming capilaries that serve the cells of the animal. The capillaries join, forming larger vessels. Blood is returned to the aortic arches through the dorsal vessel, which runs along the top of the digestive tract.