Why is the origin of mesoderm from hypoblast in some groups not regarded as a secondary adaptation? |
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The prospective endoderm displaces the hypoblast and the mesoderm forms a layer between ectoderm and endoderm. |
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This cell group often splits into an upper layer, the epiblast, and a lower layer, the hypoblast. |
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Using Lankester's terms epiblast, hypoblast and mesoblast for the embryonic germ layers, Balfour described chick ectoderm and endoderm for the first time in English. |
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Why then, asks Balfour, are hypoblast and epiblast continuous? |
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Further differentiation produces a thin layer of cells, called the hypoblast, between the inner cell mass and the cavity. |
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The cells of the primitive embryoblast differentiate into two layers, the epiblast and the hypoblast. |
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Gastrulation begins dorsally with involution of deep blastoderm cells to form an outer epiblast and inner hypoblast. |
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The lower layer of the pre-gastrulating chick embryo is an extra-embryonic tissue made up of two different cell populations, the hypoblast and the endoblast. |
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A Hypoblast is a major disappointment in partydom and should be avoided at all costs in the future. |
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