The uninjured blastomere first gives rise to a half-embryo. After this has been accomplished, other changes take place that “reorganize,” according to Roux, the material of the injured half in such a way that the missing half of the embryo is formed by a process that Roux calls “post-generation.” This process can be studied only by means of sectioning the embryos, and since the eggs may be injured to a varying extent, there must be some uncertainty in making out the sequence of events. It is found that the yolk of the injured blastomere is vacuolated in places, and that the protoplasm in the path of the needle has been killed (Fig. 61, _A_). Irregular pieces of chromatin are found in the protoplasm, which seem to come from an irregular breaking up of the nucleus. The changes that lead to the reorganization of the injured half may take place at different times in different eggs. Roux describes three kinds of reorganization phenomena. The first includes the formation of new cells in the injured half. Nuclei, surrounded by finely granular protoplasm, appear in the protoplasm of the injured blastomere. These nuclei arise from two sources: in part from the scattered chromatin of the injured blastomere itself, and in part from nuclei, or from cells without walls that have emigrated from the developing half. Around these nuclei, as centres, the protoplasm (with its contained yolk) of the injured half breaks up into cells. This cellulation of the yolk may take place in different eggs at different times. In some cases it may not have appeared as late as the gastrula stage of the uninjured half; in others, it may take place at the time when the uninjured half is segmenting.[110] The formation of the cells in the injured half begins always near the developing half, and extends thence into the injured parts. The new cells are of different sizes, but are larger than those of the uninjured half. The cellulation of the yolk takes place only in the least injured parts of the protoplasm. Where the protoplasm and yolk have been much injured, they are changed over by the second method of reorganization. This part of the blastomere is either actually devoured by wandering cells, or is slowly changed under the influence of the neighboring cells, so that it becomes a part of these cells. The surface of the injured half is covered over by ectoderm that grows directly from the developing half (third method of reorganization),--at least this happens where the protoplasm has been much injured. In other parts of the injured half the new cells that have appeared in this part, and that lie at the surface, become new ectoderm.