The initial site of gastrulation is nearly always opposite the site of polar body extrusion, on the vegetal pole of the animal 11 . And of course the end result of gastrulation - a tube with ectoderm ...The initial site of gastrulation is nearly always opposite the site of polar body extrusion, on the vegetal pole of the animal 11 . And of course the end result of gastrulation - a tube with ectoderm lining the outside and endoderm lining the inside with mesoderm or mesenchyme in the middle - is clearly homologous among planulozoans.
