Page:First steps in mental growth (1906).djvu/37



These movements, as the name indicates, are supposed to arise independently of any perceptible external stimulus. The exciting cause of the movement is within the organism, and originates "exclusively in the nutritive and other organic processes that go on in the motor centers of the lowest rank." To illustrate, Preyer found in his observations of the developing chick in the egg that from the beginning of the fifth day,

"the creature moves of itself. Here occur first only movements of the trunk, then also of the extremities and head…without the least change in the surroundings and long before the reflex excitability is present at all." Continuing Preyer writes, "There is nothing left but to assume a cause of the impulsive (automatic) movements that is internal, given in the organic constitution of the motor ganglionic cells of the spinal marrow, and connected, in the early embryonic stages, with the differentiation and the growth of those structures and of the muscular system. With the formation of the motor ganglionic cell in the spinal marrow and cervical marrow a certain quantity of potential energy must accumulate, which, by means of the flow of the blood or of lymph, or possibly through the rapid formation of tissue, is, with remarkable ease, transformed into kinetic energy." This potential energy which has been