Agassiz, AG uh see, Louis (1807-1873), was a Swiss-born naturalist who studied many kinds of animals in Europe and America. He became noted for his work on both modern and fossil forms of fishes. He established a zoological laboratory on an island in Buzzards Bay off the coast of Massachusetts to provide a place to study animals in their natural surroundings. Agassiz believed that animal species do not change, and he criticized Charles Darwin's theories on evolution. As a geologist, Agassiz showed that glaciers once covered large areas of the earth.