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Von Baer studies the embryo development in different vertebrates. The vertebrates include Fish, Frog, Tortoise, Pigeon, Chimpanzee and Man. The early stages of embryos development of above animals close are similarity with each other. It is difficult to separate them if the embryos were mixed. But the embryos differ in the final stages due to the formation of specialized characters. The similarity of early embryonic development indicate that the above animals have common ancestors.