Definition of "ectoblast" [ec•to•blast]

• The outer layer of the blastoderm; the ectoderm or epiblast (noun)

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• "The former is often also called the ectoblast, or epiblast, and the latter the endoblast, or hypoblast."
• "The entire ectoderm arises from the first, second and third micromere quartets (collectively, the 'ectoblast')."
• "When the mesoblast has become thus infinitely subdivided into hundreds of minute spheres, the ectoblast bursts, and the new generations of cells thus set free collect in that part of the egg where the embryonic disk is to arise."