A review and interpretation of previous observations and experiments. The investigations deal, in general, with the degree of organization of the Protozoa, and specifically with the structure and function of a remarkable system of fibrils connecting the locomotor organs (mem-branelles) and cirri of Euplotes and other ciliates. Cutting the body of Euplotes at various points and thereby serving the fibrils, which was accomplished with the micro-dissector of Barber and Chambers, causes disorganization of the animal''s movements; while any incisions which did not sever the fibrils failed to do so. The author concludes therefore that the fibrils are coordinating in function rather than supporting or muscular. A detailed description is given of cilia and mem-branelles.