Gill clefts and notochord appear in the embryonic development of all vertebrates from fishes to mammals. This supports the theory of

Options

A. Recapitulation
B. Metamorphosis
C. Biogenesis
D. Abiogenesis

Answer

**Step-by-Step Solution:**

1. **Understanding Key Terms:**
- **Gill Clefts:** These are the external openings that develop into gill slits, which are present in the embryonic stages of vertebrates, including primitive fishes like sharks.
- **Notochord:** This is a cartilaginous skeletal rod found in the embryonic development of vertebrates, providing support to the developing embryo.

2. **Observing the Development Across Vertebrates:**
- During the embryonic development of various vertebrates, from fishes to mammals, both gill clefts and notochord are present. This indicates a common developmental pathway among these species.

3. **Identifying the Relevant Theory:**
- The presence of gill clefts and notochord in the embryonic stages suggests that these features are remnants of ancestral traits. This aligns with the theory of recapitulation, also known as the biogenetic law.

4. **Explaining the Theory of Recapitulation:**
- Proposed by Ernst Haeckel in 1866, the theory states that the development of an organism (ontogeny) reflects the evolutionary history of its ancestors (phylogeny). In simpler terms, "ontogeny recapitulates phylogeny."

5. **Evaluating Other Options:**
- **Metamorphosis:** This refers to the transformation from larval to adult forms, which does not apply here.
- **Biogenesis and Abiogenesis:** These terms relate to the origin of life, not embryonic development.

6. **Conclusion:**
- Given that gill clefts and notochord are present during the embryonic stages of vertebrates and reflect ancestral traits, the correct answer is the theory of recapitulation.

**Final Answer:**
The theory of recapitulation (biogenetic law).

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