The presence of gill slits, in the embryos of all vertebrates, supports the theory of

Correct option (a) biogenesis 

Explanation

The theory of recapitulation' or 'Biogenetic law', propounded by Haeckel states that an individual organism in its development (ontogeny) tends to repeat the stages passed through by its ancestors (phylogeny). During the life history of frog, tadpole larva resembles fishes, the ancestors of Amphibia.  The presence of gill clefts in venebrate embryo provides a strong evidence in support of organic evolution.

Correct option: (b) recapitulation

Explanation:

In the embryos of all vertebrates, the presence of gill slits supports the theory of recapitulation (repeating the early stages of embryogenesis in earlier evolved animals).