 Since many of the earlier sources are no longer extant, or remain only fragments, Ovid's version of the myth has been the most lasting and influenced most later works.Early Greek sources have it that Philomela was turned into a swallow, which has no song; Procne turns into a nightingale, singing a beautiful but sad song in remorse.Later sources, among them Ovid, Hyginus, and the "Bibliotheca" of Pseudo-Apollodorus, and in modern literature the English romantic poets like Keats write that although she was tongueless, Philomela was turned into a nightingale, and Procne into a swallow.