#germ_layer  (embryology) any of the 3 layers of cells differentiated in embryos following gastrulation
  supertype:  #embryonic_tissue__embryonictissue  tissue in an embryo
  subtype:  #ectoderm__exoderm  the outer germ layer that develops into skin and nervous tissue
     subtype:  #neural_tube  a tube of ectodermal tissue in the embryo from which the brain and spinal cord develop
  subtype:  #mesoderm__mesoblast  the middle germ layer that develops into muscle and bone and cartilage and blood and connective tissue
     subtype:  #chordamesoderm__chordomesoderm  the area of mesoderm that forms the notochord
     subtype:  #mesenchyme  mesodermal tissue that forms connective tissue and blood and smooth muscles
  subtype:  #endoderm__entoderm__endoblast__entoblast__hypoblast  the inner germ layer that develops into the lining of the digestive and respiratory systems

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