The psychological phenomena which we directly observe in the formation of the blastula are partly sensations, partly movements, of this community of cells. The movements may be divided into two groups: (1) the inner movements, which are always repeated in substantially the same manner in the process of ordinary (indirect) segmentation of cells (formation of the axis of the nucleus, mitosis, karyokinesis, etc.); (2) the outer movements, which are seen in the regular change of position of the social cells and their grouping for the construction of the blastoderm. We assume that these movements are hereditary and unconscious, because they are always determined in the same fashion by heredity from the earlier protist ancestors. The sensations also fall into two groups: (1) the sensations of the individual cells, which reveal themselves in the assertion of their individual independence and their relation to neighboring cells (with which they are in contact, and partly in direct combination, by means of protoplasmic fibres); (2) the common sensation of the entire community of cells, which is seen in the individual formation of the _blastula_ as a hollow vesicle. The causal interpretation of the formation of the blastula is given us by the biogenetic law, which explains the phenomena we directly observe to be the outcome of heredity, and relates them to corresponding historical processes which took place long ago in the origin of the earliest protist-coenobia, the blastæads. But we get a physiological and psychological insight into these important phenomena of the earliest cell-communities by observation and experiment on their modern representatives. Such permanent cell-communities or colonies are still found in great numbers both among the plasmodomous primitive plants (for instance, the paulotomacea, diatomacea, volvocinæ, etc.) and the plasmophagous primitive animals (the infusoria and rhizopods). In all these coenobia we can easily distinguish two different grades of psychic activity: (1) the cell-soul of the individual cells (the "elementary organisms") and (2) the communal soul of the entire colony.