ABSTRACT
The range of potency of individual germ-regions can be demonstrated in different ways. One way is by the redistribution of the germinal materials. If a particular part possesses only a limited potency, by virtue of which it can form one definite organ alone, then redistribution of the materials must result in a disturbance of development. Development must either come to a complete standstill, or it must produce an irregular confusion of tissues and organs, instead of a harmonious whole. Assuming that in cleavage the potency of individual blastomeres may change, then by the third cleavage, the endo-mesodermal cytoplasm and the endo-mesodermal nuclei would be separated from the animal or ectodermal cytoplasm, with its ectodermal nuclei. In typical regulative eggs the limits of potency of individual regions of the young germ are manifestly greater than the normal performance of these parts. The so-called mosaic eggs give at least at first sight a very different impression.
