Eye Anatomy: Plica Semilunaris and Vestigial Organs
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Questions and Answers

What characteristic describes the plica semilunaris?

  • A respiratory organ
  • A vestigial structure in the eye (correct)
  • A structure in the inner ear
  • A dark, opaque membrane
  • How many vestigial organs do humans have?

  • 300
  • 180 (correct)
  • 120
  • 50
  • What did Weidersheim call humans due to the presence of vestigial organs?

  • Evolving organisms
  • Living fossils
  • Biological time machines
  • Moving museums of antiquities (correct)
  • What term describes the sudden appearance of vestigial organs in developed conditions?

    <p>Atavistic organs</p> Signup and view all the answers

    What is an example of a connecting link in the evolutionary path?

    <p>Peripatetic between annelida and arthropoda</p> Signup and view all the answers

    Study Notes

    Plica Semilunaris

    • A whitish, translucent membrane that lines the inner eyelids of birds and some mammals, including humans
    • Also known as the third eyelid, it can be drawn across the eye to protect it from dust and keep it moist
    • In some mammals, the plica semilunaris becomes vestigial and is reduced to a small fold of conjunctiva

    Vestigial Organs

    • Humans have approximately 180 vestigial organs, which are remnants of ancestral traits that have lost their original function
    • These organs are often referred to as "moving museums of antiquities" due to their historical significance

    Atavistic Organs

    • Atavistic organs are vestigial organs that suddenly reappear in developed conditions, often as a result of genetic mutations
    • Examples of atavistic organs include extra toes in humans
    • Atavistic organs are often seen as a reversion to a more ancestral state
    • Connecting links are organisms that possess characteristics of two different groups, serving as transitional forms
    • Examples of connecting links include peripatus between annelida and arthropoda, and prototherians between reptilia and mammalia
    • Connecting links provide evidence of evolutionary relationships between different groups of organisms

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    Description

    Explore the plica semilunaris, a whitish membrane in the eye, and learn about vestigial organs in humans. Discover the functions and characteristics of these anatomical structures.

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