Figure 48.

During the regeneration of H. vulgaris, a cellular cluster first establishes a spherical arrangement consisting of a hollow cellular double layer. This spheroid's regeneration can be described by three phases with saw tooth like oscillations – the radius and the second, third Fourier modes are depicted in (a). The transition from phase II to III shows a transition to non-uniform tissue elasticity as the pressurized cell ball is stronger deformed (red line) as the relaxed one (blue line). (b) Orientation of the hydra head with respect to the direction of a temperature gradient across the cell aggregate. During the transition from phase I to II, the axis is locked. Small temperature gradients applied from the beginning are sufficient to significantly affect the orientation of the head (yellow squares, red triangles) which is a signature of the system's critical state. Later, application of a temperature gradient does no longer result in an overall reorientation (blue circles). Images were adapted from [584] (a) and [497] (b) (with permission from Albrecht Ott).