 The model for a collection of metamorphosis myths derived from a pre-existing genre of metamorphosis poetry in the Hellenistic tradition, of which the earliest known example is Boio(s)' "Ornithogonia"—a now-fragmentary poem collecting myths about the metamorphoses of humans into birds.There are three examples of "Metamorphoses" by later Hellenistic writers, but little is known of their contents.The "Heteroioumena" by Nicander of Colophon is better known, and clearly an influence on the poem—21 of the stories from this work were treated in the "Metamorphoses".