242 EDWIN G. BORING 



course by means of longitudinal muscles, which warp the worm 

 along its long axis, and thus steer it to one side. It is quite 

 possible that these muscles, after the continued contraction 

 involved in prolonged movement to one side, become cramped, 

 and that there follows what is probably a natural physiological 

 co-ordination, when the muscles on the other side contract 

 suddenly and strongly, stretching the fatigued muscles. This 

 explanation involves the assumption of a simple physiological 

 co-ordination, but it avoids the implication of a complex con- 

 sciousness. Nor is it really incompatible with Pearl's sugges- 

 tion that it shows " the effect of the organism as a whole upon 

 its reflexes." 



Let us carry further the analogy to muscular cramp. As 

 the amateur agriculturist works farther and farther along the 

 row of potatoes, he pauses oftener and oftener to stretch until 

 a certain point is reached; thereafter, provided the stimulus is 

 strong enough to compel a continuation of the work, he pauses 

 less and less often and presently not at all. The muscles ' ' get set ;" 

 he now feels as if he could not straighten out. A similar phe- 

 nomenon, although not strictly analogous, can be seen in con- 

 tinued walking, where the rests for the unaccustomed walker 

 become more and more numerous, until at last, if he continues, 

 the walker " strikes his stride " and does not rest again. 9 Pro- 

 ceeding upon this analogy, we should expect the compensatory 

 movements of the planarian to increase up to a certain point, 

 then decrease, finally dropping out altogether, provided, of 

 course, that the animal remains active for a sufficiently long time. 



The increase in compensatory movement appears in Table 

 III. Here we must consider the percentages based upon angular 

 movement, as those based upon linear movement largely exclude 

 the effect of abrupt turns and were for that reason used in con- 

 sideration of light-adaptation. There is shown, on the average, 

 a reduction of turning in the D-direction from 649I to 2%. 

 This reduction may be considered as due in part to light -adap- 

 tation and in part to an increase in compensation. We have 

 already considered that the effect of light-adaptation upon the 



9 The writer has a detailed record of a fifty-mile walk, taken by two persons, 

 without any systematic practice in the preceding six months. The stops for rest, 

 although not numerous, became more and more frequent throughout the first 

 part of the route, until the last twenty-two miles, during which no stops at all 

 were made. In this last stage the pauses for water or for inquiries were accom- 

 panied by a continuation of the walking movements with the legs. 



