State and explain Huckel' s rule with an example .

Explanation

Recapitulation theory (Biogenetic law) This theory was put forward by Von Baer (1828) and Haeckel called it biogenetic law. It states that ontogeny repeats phylogeny, i.e. every organism during its development repeats in abbreviated form, the evolutionary history of its race.
However, Haeckel believed that development stages of an embryo show development stage of its ancestral adults. It is not true. An embryo recapitulates the embryonic stages of its ancestors and not the evolutionary stages of its adults. The frog during its development passes through a fish-like tadpole stage which shows that it descended from a fishh-like ancestor.