Questions and Answers
What characteristic describes the plica semilunaris?
A vestigial structure in the eye
How many vestigial organs do humans have?
180
What did Weidersheim call humans due to the presence of vestigial organs?
Moving museums of antiquities
What term describes the sudden appearance of vestigial organs in developed conditions?
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What is an example of a connecting link in the evolutionary path?
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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
- 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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