The manifold gradation of vital movement which we find everywhere in the higher organisms is not without expression even in the protist realm. In this respect the chromacea, the simplest forms of vegetal monera, and the bacteria, which we regard as corresponding animal forms, developed from the former by metasitism, are of great interest. As microscopic scrutiny fails to detect any purposive organization in these unnucleated cells, and it is impossible to discover different organs in their homogeneous plasma-body, we have to look upon their movements as direct effects of their chemical molecular structure. But the same must be said also of a number of nucleated cells, both among the protophyta and the protozoa; only in this case the structure is less simple, in so far as both the nucleus itself and the surrounding cell-body exhibit, in indirect division, complicated movements in the plasm (caryokinesis). Apart from these, however, there is nothing to be seen in many unicellular beings (_e.g._, paulotomea, or calcocytea) that we need call "vital movement." On the border between the organic and inorganic worlds we have, as regards movement, the simplest forms of the chromacea, chroococcacea. We can see no vital movement in these structureless particles of plasm except slight changes of form, which occur when they multiply by cleavage. The internal molecular movements of the living matter, which effect their simple plasmodomous metabolism and growth, lie beyond our vision. The reproduction itself, in its simplest form of self-cleavage, seems to be merely a redundant growth, exceeding the limit of individual size for the homogeneous plasma-globule (_cf._ chapters ix. and x.). The great majority of the protists have the appearance of real, nucleated cells. Hence we have to distinguish two different forms of movement in the unicellular organism--the inner movement in the caryoplasm of the nucleus and the outer in the cytoplasm of the cell-body; the two enter into close mutual relations during the remarkable process of partial resolution of the nucleus (caryolysis). In this modification and partial dissolution of their constituents we observe, during indirect cell-division, certain complicated movements (the significance of which is as yet entirely unknown), that are accomplished by both the granules of chromatin and the threads of achromin, and which are comprised under the head of nuclear movements (caryokinesis). It has lately been attempted to explain them on purely physical principles. The same may be said of the internal flow of the plasm which we find in the plasmodia of the amœbæ and mycetozoa, and in the endoplasm of many of the protophyta and protozoa.