. Carnegie Institution of Washington publication. 5 TMK BEHAVIOR OF LOWEK ORGANISMS. the organism is necessarily turned with anterior end toward the source of stimulus; then its usual forward movements take it toward the source of stimulus (positive taxis or tropism). Loeb lays especial stress on the direction from which the stimulus comes, as it is this that determines which side shall be most strongly affected by the stimulus ; otherwise the theory as he sets it forth is essentially like that held by Verworn. Both these authors apply this schema to the move- ments of organisms to and from ma
. Carnegie Institution of Washington publication. 5 TMK BEHAVIOR OF LOWEK ORGANISMS. the organism is necessarily turned with anterior end toward the source of stimulus; then its usual forward movements take it toward the source of stimulus (positive taxis or tropism). Loeb lays especial stress on the direction from which the stimulus comes, as it is this that determines which side shall be most strongly affected by the stimulus ; otherwise the theory as he sets it forth is essentially like that held by Verworn. Both these authors apply this schema to the move- ments of organisms to and from many sorts of stimuli, making it a general formula for taxis or tropisms. Verworn says (1899, p. 503): Thus the phenomena of positive and negative chemotaxis, thennotaxis, photo- taxis and galvanotaxis, which are so highly interesting and important in all or- ganic life, follow with mechanical necessity as the simple results of differences in biotonus, which are produced by the action of stimuli at two different poles of the free living cell. In the present series of papers the writer proposes to examine the behavior of a number of lower organisms, in order to determine. FIG. 2.* whether the reactions to the usual stimuli take place in accordance with this tropism schema or not, and if not, to determine the real nature of the reaction method. In this first paper we shall deal with reactions to heat and cold. In his recent series of papers on the reactions of infusoria to heat and cold, Mendelssohn (1902, a, b, c} develops a theory of thermotaxis in accordance with the general theory of tropisms, above set forth. In an earlier paper (Jennings, 1899) the present author, on the other hand, * FIG. 2.—Diagram of a positive reaction, according to the tropism schema. A stimulus coining from the direction indicated by the arrows to the right acts upon the organism a. The effect of the stimulus is to cause the motor organs directly affected by it to contract less strongly, as indicated
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