io8 Journal of Comparative Neurology and Psychology. 



fail to see the method exemplified. If he were watching a 

 chick pecking at a variety of objects and giving signs of disgust 

 when it had seized a nauseous substance he would doubtless re- 

 gard the process as one of trial and error whatever name he 

 might apply to it. A study of the conduct of much lower or- 

 ganisms would disclose many cases almost equally evident. 

 The lives of most insects, crustaceans, worms, and hosts of low- 

 er invertebrate forms including even the protozoa show an 

 amount of busy exploration that in many cases far exceeds that 

 made by any higher animal. Throughout the animal kingdom 

 there is obedience to the Pauline injunction, "Prove all things; 

 hold fast that which is good." 



The trial and error method is set off by Jennings in sharp 

 contrast to the usual scheme of tropic reaction. "The trop- 

 ism," he says, "leads nowhere; it is a fixed, final thing, like a 

 crystal." And elsewhere: "This method of trial and error, 

 which forms the most essential feature of the behavior of these 

 lower organisms, is in complete contrast with the tropism 

 schema, which has long been supposed to express the essential 

 characteristics of their behavior. The tropism was conceived as 

 a fixed way of acting, forced upon the organism by the direct 

 action of external agents upon its motor organs. There was no 

 trial of the conditions; no indication of anything like what we 

 call choice in the higher organism; the behavior was stereo- 

 typed." (p. 250). If the term trial and error is used in the wide 

 sense here employed I cannot but think that the distinction be- 

 tween the method so designated and the orthodox scheme of 

 tropisms is not, after all, so wide as it at first appears. The 

 motor reaction of Parameciuin is certainly a fixed way of acting 

 brought about almost inevitably by certain factors of the envi- 

 ronment. Its behavior is certainly as stereotyped as that of any 

 organism whose reactions are definitely known. Its reactions 

 are "forced movements" in the untechnical sense of this ex- 

 pression, and there is no more evidence of choice in its conduct 

 than in the contraction of a muscle; for we can scarcely speak 

 of choice in a creature that reacts in oneway to all sorts of stim- 

 uli. On the other hand the trial and error method may be ex- 



