276 MORRIS M. WELLS 



therefore, are the reverse of those in sea-water with regard to 

 these three factors, and in the normal hfe cycle of such anadro- 

 mous fishes as the salmon, this reversal in reaction must occur 

 at least twice, once when the fishes leave the fresh water streams 

 for the ocean, and again when they return. With species of 

 salmon that breed more than once, the reversal must occur more 

 often. 



There are two general complexes of factors to be considered 

 in an attempted explanation of the reactions of the anadromous 

 fishes, namely, the fish and the environment. Both are made 

 up of physico-chemical factors which are measurable, and to a 

 large degree quantitatively. Of the two complexes, that of 

 the living organism is least understood and perhaps, because 

 it is much more variable and changing than the environmental 

 complex, which, especially in the case of the sea-water, varies 

 hardly at all. For the fishes to live normally in the environ- 

 ment there must exist between the two complexes a more or less 

 complete equilibrium. A disturbance of this equilibrium re- 

 sulting from a change in either of the complexes, will, if great 

 enough or long enough continued, result in the death of the 

 fishes unless by their reactions thej^ seek out another environ- 

 ment which allows their physiological processes to proceed nor- 

 mally. It ^hould be emphasized that the only mode of readjust- 

 ment is through the proper, reaction, either physiological or motile 

 upon the part of the fishes, since the environment is much the 

 more stable complex, and there is a great deal of evidence to show 

 that of the two possible reactions upon the part of the living 

 organism, the motile reaction is much more likely to occur than 

 the physiological readjustment, i.e., acclimatization. The data 

 presented in this paper and the one preceding (Wells '15a) as well 

 as that by Shelf ord and Allee ('13) and Shelf ord and Powers 

 ('15) show that fishes will react to environmental factors in a 

 way that will tend to remove them from detrimental conditions, 

 long before the adjustment becomes a matter of life and death. 

 Thus we find the salmon leaving the fresh water for the ocean, 

 when, as will be pointed out later, it has been shown (Daj^ '87) 

 that remaining in the fresh water for the entire life cycle would not 



