What is it called when an artist creates a new work that's based on an original work or idea?

Read the excerpt from chapter 28 of moby-dic. it had previously come to me that this ivory leg had at sea been fashioned from the polished bone of the sperm whale’s jaw. how is the fact that ahab’s leg is made from whale bone significant to the novel’s theme of man versus nature? it signifies that ahab has pitted himself against nature in an effort to dominate it. it signifies that ahab lives a life in harmony with the natural world. it signifies that ahab has made a choice to surrender to the power of the whales he hunts. it signifies that ahab see himself as an equal and dependent part of a greater whole.