. Contributions to the study of the behavior of lower organisms. Physiology, Comparative; Infusoria; Amoeba; Irritability. REACTIONS TO HEAT AND COLD IN THE CILIATE INFUSORIA. To explain the movements of organisms toward or from a source of stimulus, we find given almost universally in one shape or another a certain general formula. This is the schema set forth, with unessen- tial variations, by Verworn (1S99, pp. 500-502) for the orientation of a ciliate or flagellate infusorian to a one-sided stimulus, and by Loeb (1S97, PP- 439~442) for the tropisms of organisms in general. Essen- tially, t
. Contributions to the study of the behavior of lower organisms. Physiology, Comparative; Infusoria; Amoeba; Irritability. REACTIONS TO HEAT AND COLD IN THE CILIATE INFUSORIA. To explain the movements of organisms toward or from a source of stimulus, we find given almost universally in one shape or another a certain general formula. This is the schema set forth, with unessen- tial variations, by Verworn (1S99, pp. 500-502) for the orientation of a ciliate or flagellate infusorian to a one-sided stimulus, and by Loeb (1S97, PP- 439~442) for the tropisms of organisms in general. Essen- tially, the schema is as follows : An agent acting upon the organism from one side causes the locomotor organs of that side to contract either more strongly or less strongly than those of the opposite Fig. I.* In the former case (Fig. i) the animal is turned away from the source of stimulus, till it comes into a position in which the motor organs of the two sides are similarly affected. Then progressing straight for- ward, it of course moves away from the source of stimulus (negative taxis or tropism). If the motor organs on the side most affected ai'e caused to contract less strongly than those on the opposite side (Fig. 2) *FiG. I.—Diagram of a negative reaction of an organism, according 10 the tropism schema. The motor organs which act more eflfectively are shown more heavily drawn. The more pointed end is the anterior. A stimulus is supposed to impinge upon the organism a from the direction indicated by arrows; this causes the motor organs directly affected by the stimulus to beat more strongly, as indicated by the darker shade. The result is to turn the anterior end in the direction indicated by curved arrows. The organism thus occupies successively the positions a, b, c, finally coming into the position d. Here the motor organs of the two sides are equally affected by the stimulus, hence there is no further cause for a change of position. The usual forward motion of the o
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