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THE AMERICAN NATURALIST [Vol. XLI 



haphazard, in character. The phenomena are thus similar to those 

 shown in the "learning" of higher organisms, save that the modifica- 

 tions depend upon less complex relations and last a shorter time. 



Each organism is found to exhibit a set of actions made up, in the 

 case of the lower organisms, of a few factors combined in various ways 

 in a coordinated system which Professor Jennings designates as "the 

 action system." For the term "motor reaction" employed in his 

 earlier papers the phrase "avoiding reaction" is now used to designate 

 the stereotyped method of reaction of Infusoria to most stimuli. The 

 author rejects the local action theory of tropisms as a "more or less 

 artificial construction, made by combining certain elements of behavior 

 and omitting others that are of most essential significance." In its 

 place he proposes the method of "trial and error" as an explanation 

 of behavior. The stimulus interferes with definite internal processes 

 occurring in the organism and this interference causes a change in 

 behavior and varied movements which subject th(^ organism indis- 

 criminately to many different conditions. It merely acts in all sorts 

 of ways possible to it. When oih- of these new conditions thus met 

 relieves the organism from the existin*;; int(>rferenee with its life proc- 

 esses, the trials cease. 



As a second cornerstone in the formulation of behavior we find the 

 law of "resolution of physiological states" thus stated: "The resolu- 

 tion of one physiological state into another becomes easier and more 

 rapid after it has taken place a number of times." It appears that 

 even in Stentor and Vorticella repetition of an action brings the second 

 step in a sequence in behavior more quickly upon the first. Here lie 

 the foundations of the phenomena which are usually designated as 

 habit formations, memory and learning, and the question may well 

 be asked w hether they are not coextensive with life and based funda- 

 mentally on the physical and chemical structure of colloids. 



C. A. K. 



Modernized Darwinism.^ — Professor Guenther has written a very 

 readable book on Darwinism and allied biological problems which 

 the tyro will find quite intelligible. The translation seems good 

 and the publishers have done their part well. The treatment of 

 the subject is rather novel, moSt of the chapters being divided tax- 



' C. Guenther. Darwinism and the Problems of Life. Translated from the 

 third edition by Joseph McCabe. London: A. Brown & Co., 1906, Dutton 

 & Co., New York, American agents. 8vo, 439 pp. 



