for at the very moment when the leading fish had reached that neighbouring land , the land had risen up on a wave between him and the sky ; and he had seen , in perfect and unmistakable silhouette , the thing on the fish 's back reveal itself as a human form - a human form which stepped ashore , turned with a slight inclination of its body towards the fish and then vanished from sight as the whole island slid over the shoulder of the billow .