3o8 BEHAVIOR OF THE LOWER ORGANISMS 



inore adequate way than the simple local reaction of the part stimu- 

 lated. 



Such behavior apparently represents not a primitive condition, but 

 a product of development. How has it been brought about ? 



It is evident that the operation of the law of the readier resolution of 

 physiological states after repetition, taken in connection with behavior 

 by selection from varied movements, would in course of time produce 

 such reactions. Let us suppose that the original reaction to a stimulus 

 at the anterior end was simply the production of a change resulting in 

 varied movements, according to the principles governing the actual 

 reactions of Paramecium. These varied movements would include for- 

 ward as well as backward motion. The forward movement would in- 

 duce still further stimulation, hence it would be changed. The back- 

 ward movement would give rehef from stimulation, hence would not be 

 changed (till internal conditions require). Hence after stimulation at 

 the anterior end the physiological states induced will always be resolved 

 finally into that state corresponding to backward movement. This 

 resolution will in time become spontaneous ; the physiological state due 

 to stimulation at the anterior end will pass at once into that producing 

 movement backward. Trial movements will no longer occur, but the 

 organism will respond at once by backward motion. A similar exposi- 

 tion will account, mutatis mutandis, for other locaHzed reactions. 



Whether this condition has been brought in the way above sketched 

 or not, its existence is evidently a fact of great importance.- It is a step 

 forward from the pure "trial movement" condition. Wherever the or- 

 ganism can react in this manner, and this will meet the conditions 

 equally well, we may expect such behavior in place of repeated trials. 

 In higher organisms especially we find this behavior playing a large part. 

 Such organisms could not be expected, for example, to orient to gravity 

 or to light rays by trial movements, as the infusoria do, but rather to 

 turn directly toward or from the source of action of the stimulating 

 agent. This is, of course, known in many cases to be true. 



But under many circumstances the reaction by trial is surer, though 

 less rapid, than that depending directly on the localization of the stimu- 

 lus, so that we find the trial method much used even by higher organ- 

 isms (see Chapter XII). Further, the more direct reactions due to pre- 

 cise localization are again combined as elementary factors to produce 

 behavior based on the method of trial, as when the flatworm turns toward 

 and "tries" any source of weak stimulation, accepting or rejecting it 

 finally, according as it proves fit for food or not. Thus we have be- 

 havior rising to a higher degree of complexity, — the method of trial in 

 the second or third degree, as it were. Examples of this character are 

 abundant. 



