An earthworm has five aortic arches, each functioning similarly to a heart. The aortic arches have the purpose of pumping blood through the dorsal and ventral blood vessels. The dorsal blood vessel carries blood to the front of the body, while the ventral vessel carries blood to the back.
Earthworms exchange carbon dioxide and oxygen through their skin because they lack lungs. An earthworm's skin must be kept moist in order to breathe. A combination of mucus and dampened soil prevents the worm from desiccating. Earthworms are nocturnal in part because the cooler air helps maintain moisture within the environment.