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THE AMEBIC AX NATURALIST [Vol. LII 



that we make for our own purposes. ' ' We have seen that 

 the essence of the animal is its activity. Its life is a 

 continuous collision with the environment and a bombard- 

 ment by the environment, with changes which tend to re- 

 lieve the disturbances. This is particularly true of free- 

 living animals, and is indirectly so, even of sedentary and 

 sessile kinds. This radiating activity of the animal, and 

 the direct convergent influence of the environment on the 

 animal, is the basis for the friction and interaction which 

 exists between the organism and the environment. There 

 are, therefore, definite zones of influence and stimulation 

 about the normal or attuned environment of the animal, 

 and with departure from these conditions locally and 

 geographically there are certain definite results (Adams, 

 '04, p. 211) : 



The new vital conditions are a cause of stimulation and with further 

 departure (beyond a certain limit) it leads to increased stimulation or 

 to unfavorable conditions. This results in retarded growth, development, 

 and reproduction of the oi-aui>,n a- a whyle. Thus the end results of 



(Adams, '15, pp. 8 9) : 



Thus departure from the optimum toward an increase or a decrease, 



(Adams, '13, p. 98) : 



aridity, and the lack of oxygen may be cited as examples. Such effects 

 have an important bearing upon the subject of physical and chemical 

 li.niitinn factors which influence individuals. [Cf. Shelford, '11, pp. 

 598-599.] 



I would now modify my preceding quotations so as to 

 definitely discard the old idea of the optimum, 6 in harmony 



