Before revision: Vertebrates (such as reptiles, some fish, and most birds) reproduce with internal fertilization through cloacal copulation (see also hemipenis), while mammals copulate vaginally .
After revision: Vertebrates (such as reptiles, some fish, and most birds) reproduce with internal fertilization through cloacal copulation (see also hemipenis), while placental mammals copulate by inserting the male's penis into the female's vagina .