Subcortical Rotation:

Altering the Normal Process

The picture at right, taken from work by Black and Gerhart (198?) demonstrates one of the ways in which the normal rotation process can be overridden, producing dramatic results. Here embryos were centrifuged after rotation had begun, presumably producing a second relative displacement of the cortex and underlying material in the fertilized Xenopus egg. The second displacement apparently is sufficient to produce a second region capable of axis formation during subsequent development, resulting in two headed-tadppoles.