Cortical and Subcortical Changes Preceding Furrow Formation in the Cleavage of Newt Eggs

In the first cleavage of the egg of the newt, Cynops(Triturus) pyrrhogaster, some sort of preparation for the furrow formation in the cortical and subcortical cytoplasm precedes the advancing tip of the cleavage furrow. This is shown by the following facts: (1) Incisions made close to the tip of the cleavage furrow do not stop the progress of furrowing, allowing the furrow to cross the incisions and appear on the farther sides, while incisions made far enough from the furrow tip always prevent the further travelling of the furrow, (2) Displacement of the subcortical cytoplasm ahead of the furrow by rubbing with a hair loop makes the furrow bend corresponding to the width of the rubbed area, and (3) Transplantation of the subcortical material of the furrow tip to lateral parts in the same egg causes a depression in the overlying cortex at the transplanted position. The linear extension of the prepared area for the furrow formation is the longest in the animal hemisphere and it decreases in gradient towards the vegetal pole.