Earthworms do not have eyes, but they are equipped with cells that can sense changes in the intensity of light as well as cells that can respond to and measure touch. Earthworms are very primitive organisms who do not need to depend on sight to feed as they spend their lives simply moving through the soil and getting their nutrients from it.
Earthworms feed by processing nutrients out of soil along their lengthy gut track and oxygenate their blood by dissolving oxygen with their thick coats of mucous. Oxygen dissolves upon contact with this layer of mucous and passes directly into the earthworm's bloodstream.
Because worms do not depend on eyesight or other senses to guide them, they can move backward and forward with equal facility. For unknown reasons they tend to move forward, but they move in reverse with equal speed and do not suffer any reduction in digestive efficiency for doing so.
Earthworms are so simple and robust that they can survive being cut in two. One half, the rear, invariably perishes while the front, if it is strong and healthy, will survive and regenerate to its full length. This adaptive trait allows worms to survive even being partially devoured by their many predators and then go on to reproduce.