part of part of immediately preceded by immediately preceded by occurrent late gastrula stage stage 16 early organogenesis stage The embryo is elongated along the animal-vegetal axis and has thus a characteristic oblong shape. The archenteron is fully extended, even though it still does not reach the blastocoel roof. The tip of the archenteron is enlarged, rounded, and smooth, and the archenteron has begun to deflect orally. Mesenchyme cell ingression is complete. However, paired coelomic pouches and gut constrictions have not yet formed. ecao_developmental_stage