ex 3

• Vitelline membrane


  Yolk membrane surrounding the unfertilized egg
• Isolecithal egg


  Egg with evenly distributed yolk material
• Unfertilized egg


  • Surrounded by vitelline membrane
  • Yolk material evenly distributed in cytoplasm
• Fertilization membrane


  Membrane that arises immediately after sperm penetration to prevent further fertilization
• Peri-vitelline area


  Space between fertilization membrane and yolk
• Fertilized egg


  • Presence of fertilization membrane
  • Peri-vitelline area between membrane and yolk
• Cleavage


  1. Division of yolk into two equal blastomeres (holoblastic cleavage)

  2. First and second cleavages are meridional and perpendicular

  3. Third cleavage is equatorial and perpendicular to first two

  4. Subsequent cleavages become more asymmetrical, forming micro-, macro- and mesomeres
• Blastomeres


  Embryonic cells formed by cleavage of the zygote
• Morula


  Pluricellular stage where cytoplasm is completely divided over blastomeres
• Blastula


  Stage where blastomeres spread to form a monolayer around a central cavity (blastocoel)
• Gastrulation


  1. Invagination of blastomeres at vegetal pole to form ectoderm and endoderm

  2. Ingression of primary mesenchyme cells from base of archenteron

  3. Separation of second group of mesoderm cells from upper archenteron
• Archenteron


  Primitive intestine formed during gastrulation
• Ectoderm


  Outer layer of cells formed during gastrulation
• Endoderm


  Inner layer of cells formed during gastrulation
• Mesoderm


  Middle layer of cells formed during gastrulation
• Pluteus larva


  • Primarily bilateral symmetry, radial symmetry is secondary