172 BIOLOGY: GENERAL AND MEDICAL 



of behavior to new conditions. It enables the animal to 

 successfully overcome difficulties arising in the perform- 

 ance of behavior, and results in new forms of behavior. 



According to Parmelee, "it is made up of tropic, reflex, 

 and instinctive actions that have been combined in new 

 ways as a result of experience so as to constitute new forms 

 of behavior." 



If it is conceded to depend upon experience, it must 

 have its foundation in the recollection of the results of 

 previous trials, i. e., memory, or, to be more correct, in 

 associative memory. 



Loeb defines this as "that mechanism by which a stim- 

 ulus brings about not only the effects which its nature 

 and the specific structure of the irritable organ calls for, 

 but by which it brings about also the effects of other stimuli 

 which formerly acted upon the organism almost or quite 

 simultaneously with the stimulus in question." 



Such associative memory is the basis of training; any 

 animal that can be trained has associative memory, and 

 training is nothing more than the modification of behavior 

 through experience. 



"Processes which occur in the central nervous system 

 leave an impression or trace by which they can be repro- 

 duced even under different circumstances than those 

 under which they originated. . . . Two processes which 

 occur simultaneously or in quick succession will leave 

 traces which fuse together, so that if later one of the 

 processes is repeated, the other will necessarily be re- 

 peated also." 



Memory .and associative memory, like other nervous 

 phenomena, make their appearance as soon as the nervous 

 system attains to a certain complexity. Loeb says that 

 "it can be shown that infusoria, ccelenterates, and worms 

 do not possess a trace of associative memory and there- 

 fore no intelligence. . . . Certain insects have been 

 shown to display intelligence wasps, etc. Yerkes has 

 shown that certain crustaceans possess a glimmering of it. 



The greater the complexity of the central nervous 



