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What are several embryonic features that form early in the developmental stages but are...

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maddyprice | eNotes Newbie

Posted August 26, 2013 at 1:52 AM via web

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What are several embryonic features that form early in the developmental stages but are "lost" or converted to entirely new structures such as our "tail"?

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orchid101 | College Teacher | (Level 1) Associate Educator

Posted August 26, 2013 at 3:56 AM (Answer #1)

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All the multicellular organisms exhibit a common pattern of development. Their development starts from a unicellular fertilized egg or zygote. The fertilized egg after repeated cell divisions forms blastula, which finally develops into a two layered gastrula. The cavity lined by endoderm forms the archenteron, the future digestive tract. The development after gastrula stage becomes modified in different groups of animals. The early human embryo with a dorsal hollow nerve cord, a well developed notochord and a series of gill-slits represents the fundamental chordate characters. With the development of a piscine heart, paired arotic arches, primitive pronephros and a tail it resembles a fish embryo.
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orchid101 | College Teacher | (Level 1) Associate Educator

Posted August 26, 2013 at 4:38 AM (Answer #2)

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The vestigial or rudimentary organs are the useless remnants of structures or organs which might have been large and functional in the ancestors. Man alone possesses nearly 100 such vestigial structures.

(1)Vermiform appendix in man- The human appendix is the remnant of the caecum, which is large and functional in herbivorous mammals. It helps in the digestion of cellulose. But because, the descendants changed their food habits, the caecum and appendix no longer useful, gradually got reduced. (2)Muscles of external ear- complete set of muscles for bringing about these movements is present in the external ear of man but non-functional. (3)Nictitating membrane- it is completely unstrerchable. (4)Vestigial tail vertebrae- early embryo of man possesses an external tail but it is shed off much before the adulthood is attained. Rarely a child may be born with a short visible tail. (5)Wisdom teeth- the third pair of molars are vestigial, because these are last to erupt or even fail to erupt.

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