ABSTRACT
Certain divisions are often distinguished among the reactional processes. Tropisms, reflexes, instinctive acts and intelligent acts have been suggested. Tropisms, according to the conception of Loeb, consist of reactions of orientation towards an excitant, which result in making symmetrical a formerly asymmetrical stimulation. The mechanism provides for direct transmission of the energy of the excitant into motor discharge. A butterfly receives more light in the left eye; the light energy is carried to the muscles of the wings on the other side; these act more energetically until the consequent rotation places the animal face to face with the source of light; and, from that moment, since the two sides of the body receive the same quantity of energy, rectilinear flight conducts the animal towards the light.
