GastrulaArtemiaEctodermAmbystomaEmbryo, NonmammalianPleurodelesTriturusSea UrchinsMesodermEmbryonic InductionXenopus laevisXenopus ProteinsXenopusMicroscopy, Electron, ScanningGene Expression Regulation, DevelopmentalBody PatterningMorphogenesisIn Situ HybridizationMolecular Sequence DataRNA, MessengerCell DifferentiationAmino Acid SequenceBase Sequence