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THE AMEBIC AN NATURALIST [Vol. XLVIII 



ent, and others advantageous. Upon these physiological 

 characters natural selection has operated to eliminate, 

 and with time has perhaps rendered of less frequent 

 occurrence, those characters that are incompatible with 

 their conditions of existence. External form, color orna- 

 mentation, etc., while no doubt often of importance them- 

 selves are more often the advantageous or indifferent 

 correlatives of physiological or irritability types which 

 are compatible with their conditions of existence. The 

 study of irritability and response may be pursued in 

 many ways — by experiment, by observation in nature 

 alone or combined with experiment. The mapping of 

 stimulating conditions in nature, of the distribution of 

 types of irritability and response, which is one function 

 of field ecology and modern geography, can hardly fail 

 to contribute materially to the advance of knowledge in 

 many lines, including that of the physico-chemical 

 mechanism of life. The student of experimental ecology 

 has an infinite field of problems and methods thrown 

 open to him by the organization of such information 

 relative to responses. Still in our attempt to make ad- 

 vances along the line of the study of responses, we must 

 not forget that it is but one of several lines of advance, 

 all of which must sooner or later be correlated with a 

 view to broader generalization. 



April 1, 1914 



LITERATURE CITED 



Adami, J. G. ('08). Principles of Pathology; Vol. I, General Pathology. 



