ACTION OF EXTERNAL INFLUENCES. 19 



page 30.) These appear as the direct results of 

 operating causes. 



When the stress of environment exceeds the 

 limits of idioplasmic elasticity, its influence brings 

 about permanent variations, which are impercepti- 

 bly small, it is true, in the single individual, but 

 which, when the stimulus is active for a long period 

 of time in the same manner, increase to perceptible 

 magnitude. These variations are inheritable in 

 the phylogenetic sense and contribute to the for- 

 mation of varieties and species ; they always appear 

 as the results of more or less secondary reactions 

 which make their appearance with stimuli exerted 

 by external causes. 



External stimuli exerted on the organism are 

 reproduced in the idioplasm. Since the stimulus 

 is discontinued with each change of the ontogeny 

 and only the idioplasm persists, permanent varia- 

 tions are produced only in the idioplasm by those 

 conditions that produce visible transformations in 

 the mature organism. 



The phylogenetic action of external stimuli gives 

 the definite character of adaptation to the idioplasm 

 as it becomes more complex from inner causes and 

 probably these external stimuli have the power to 

 alter this impress only as new idioplasm is auto- 

 matically formed. 



If an external cause acts continuously upon a 

 phylogenetic line, the corresponding variation of the 



