Embryological support for evolution was also proposed by Ernst Heckel based upon the observation of certain features during embryonic stage common to all vertebrates that are absent in adult. For example, the embryos of all vertebrates including human develop a row of vestigial gill slit just behind the head but it is a functional organ only in fish and not found in any other adult vertebrates. However, this proposal was disapproved on careful study performed by Karl Ernst von Baer. He noted that embryos never pass through the adult stages of other animals. Aristotle believed in the theory of spontaneous generation while Louis Pasteur disproved it using the famous swan neck experiment. Lamarck believed in the theory of use and disuse of organs while Weismann cut the tails of new born mice for several generation and disproved their theory. The theory of evolution due to natural selection was supported by Charles Darwin and Alfred Wallace