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Difficulty: EasyEvidence for Evolution: Comparative Anatomy, Embryology, and Vestigial Organs

The presence of a small, non-functional fold of tissue known as the plica semilunaris (nictitating membrane) in the inner corner of the human eye is an example of which of the following?

  1. A vestigial structureAnswer
  2. B
    An analogous structure
  3. C
    A homologous structure
  4. D
    A protective camouflage adaptation

Answer

A vestigial structure
The human plica semilunaris is a vestigial structure because it represents a reduced anatomical remnant of a transparent third eyelid (nictitating membrane) that was functional in common ancestors but has lost its primary utility in modern humans.

Step-by-Step Solution

1
Analyze the functional state and history of the structure mentioned in the prompt.
The plica semilunaris in humans is a reduced, non-functional remnant of the translucent third eyelid that remains functional in birds and reptiles.
Structures that are underdeveloped and perform no major current function compared to their functional ancestors are categorized as vestigial organs.

Key Concept

Vestigial structures as anatomical evidence for evolution
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Topics

Evidence for Evolution: Comparative Anatomy, Embryology, and Vestigial Organs

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