Tissue layers that develop in the embryo

• the developing animal embryo consists of a mass of cells that are arranged in the shape of a ball
• Different tissue layers (germ layers) can be distinguished:

  ectoderm- outer germ layer

  endoderm- inner germ layer

  mesoderm germ layer between ecto and endoderm
• Diploblastic

  embryo has two germ layers: ectoderm on the outside and an endoderm on the inside
• Triploblastic

  embryo has three germ layers: ectoderm, endoderm and a mesoderm between the ectoderm and endoderm
• Animals that show radial symmetry only have two germ layers and are diploblastic
• Diploblastic animals have tissue level of organisation and do not develop organs
• All bilaterally symmetrical animals are triploblastic with three germ layers and an organ level of organisation
• All different tissues and organs of an animal develop from the three germ layers
• Ectoderm

  Develops:

  • outer protective layer
  • nervous system and sense organs
• Endoderm

  Develop: epithelial lining of digestive tract
• Mesoderm

  Develops:

  • internal organs, part of blood, muscular, reproductive systems, skeleton and connective tissue