The development of the isolated blastomeres of the ctenophore egg may seem at first sight to give support to Roux’s hypothesis, for in this case the first two cells are completely separated, and yet give rise to half-structures. Crampton’s experiments on the eggs of ilyanassa may also appear to be evidence in favor of this view. In fact, however, they give no more support to the idea of a qualitative division of the nucleus than they do to that of a qualitative division in the protoplasm, and there are some further experiments on the ctenophore egg which indicate that it is the latter rather than the former sort of division that takes place. As stated in the preceding chapter, Driesch and Morgan found that, if a part of the protoplasm of the unsegmented egg of the ctenophore is removed, an incomplete embryo develops, although the whole of the segmentation nucleus is present. Ziegler’s results show that, even after the removal of that part of the egg from which the micromeres develop, the segmentation may still be like that of the whole egg, and this shows that the egg has great powers of recuperation (at least in a symmetrical plane), so far as its protoplasm is concerned. If, however, it is true that when a part is cut off unsymmetrically the protoplasm cannot reorganize itself, then the conclusion that Driesch and Morgan drew in regard to the protoplasm will hold, provided, as seems to be the case, the smaller blastomere of the first two is large enough to produce the typical structures. The main point is this: If the protoplasm readjusts itself after the operation, so that the piece divides as a whole, a complete embryo develops; if, however, the protoplasm does not readjust itself, and the piece divides as a part, an incomplete embryo is formed. Since in both cases the same nucleus is present, and since the difference is obviously connected with a change in the protoplasm, it seems much more probable that the phenomenon of whole and half development is connected with the protoplasm and not with the nucleus.