The Emission Quanta of Characteristic X Rays.

and give rise to, cells which are more or less removed from their normal places. Thus polar bodies and ectoderm cells may be caused to form at the vegetative pole or at any other point on the surface of the egg instead of at the animal pole; nevertheless the protoplasmic portions of the yolk-containing cells return to the animal pole when centrifuging ceases unless otherwise prevented. In some instances in which centrifuging took place in the two cell stage the normal positions of protoplasm and yolk are regained in one of the cells but not in the other. All such cases indicate that it is difficult but not absolutely impossible to change the polarity of eggs and cleavage cells, and that the persistence of polarity in centrifuged eggs and the restoration of dislocated parts to their normal positions is connected with a somewhat resistent framework of protoplasmic strands which preserve the relative positions of nucleus and centrosphere in the cell axis.