The juvenile sea squirt wanders through the sea searching for a suitable rock or hunk of coral to cling to and make its home for life. For this task, it has a rudimentary nervous system. When it finds its spot and takes root, it doesn’t need its brain anymore, so it eats it! (It’s rather like getting tenure.)

Daniel C. Dennett, Précis of Consciousness Explained, Philosophy and phenomenological research, vol. 53, no. 4, 1993, pp. 889–892, p. 177