Movement of the cell surface and change in surface area during cleavage in the newt's egg.

In cleaving eggs of the newt, Cynops pyrrhogaster, the behaviour of the egg surface was analysed by observing linear and area changes in a transplanted piece of cortex which differed in pigmentation from the background. Results from the animal hemisphere showed that the surface in the cleavage plane shrank extensively in the region where the early cleavage furrow was being formed. On both sides of the cleavage plane, the surface began to shrink in a direction parallel to the cleavage furrow and to stretch perpendicularly to the furrow, simultaneously with the onset of cleavage. The nearer the grafted region was to the furrow, the greater the change. These changes continued until about the time of the appearance of unpigmented surface on both walls of the furrow, when a maximum was reached. Thereafter a slight reversal was observed. Similar changes of lesser magnitude were encountered in regions remote from the cleavage plane. The surface area decreased in the vicinity of the furrow during the early phase of cleavage and returned roughly to its original value during the late phase, while, in the distant region, only an increase occurred. Results from the vegetal hemisphere showed that little linear change of surface occurred even in the region adjacent to the furrow, while the surface area changed in the furrow region similarly to the animal half. In the vegetal hemisphere remote from the furrow, the changes took place to a lesser extent.