Endostyle is similar to

Options

A. Parathyroid
B. Thyroid
C. Thymus
D. Thalamus.

Explanation

**Step-by-Step Solution:**

1. **Understanding Endostyle**: The endostyle is a glandular structure found in certain chordates, particularly in the larval stage of organisms like amphioxus. It plays a crucial role in the metabolism and feeding of these organisms.

2. **Evolutionary Context**: The concept of ontogeny recapitulating phylogeny suggests that the development of an organism (ontogeny) reflects its evolutionary history (phylogeny). This means that structures in simpler organisms can provide insights into the functions of similar structures in more complex organisms.

3. **Metamorphosis in Amphioxus**: In amphioxus, the endostyle undergoes metamorphosis. During this process, it is involved in the secretion of substances that are chemically similar to hormones found in vertebrates.

4. **Comparison with Thyroid Gland**: The endostyle in amphioxus is functionally and chemically similar to the thyroid gland in vertebrates. The thyroid gland produces hormones such as thyroxine, which are crucial for metabolism and development.

5. **Chemical Similarity**: The endostyle secretes iodinated tyrosine molecules, which are analogous to the thyroxine hormone produced by the thyroid gland in vertebrates. This indicates that the endostyle serves a similar function in the larval stage of amphioxus as the thyroid gland does in vertebrates.

6. **Conclusion**: Based on the similarities in function and chemical composition, the endostyle is similar to the thyroid gland in vertebrates. Therefore, the correct answer to the question is that the endostyle is similar to the thyroid gland.

**Final Answer**: The endostyle is similar to the thyroid gland.

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