TROUT FLY-FISHING IN AMERICA 



pigment colors at their surface due to contraction or ex- 

 pansion of the cells. 



Bearing of Factors Upon Each Other 



( 1 ) Position of the pigment cells. 



(2) Activity of the pigment cells : 



Character of the water bottom. 

 Kind or degree of light. 

 The breeding season. 

 The age of trout. 



(3) Kind or character of food. 



(4) Character of the water bottom. 



(5) Kind or degree of light: 



Kind of day. 

 Condition of the water. 

 Season of the year. 



The Functions of the Five Factors 



Position of the pigment cells 

 {Internal factor) 



Activity of the pigment cells 

 (Internal factor) 



Kind or character of food: 

 (Internal factor) 



The function of this factor is to 

 make marked coloration possi- 

 ble, which is due to the location 

 of the pigment cells in the skin 

 and on or near the surface of the 

 scales. 



The function of this factor is to 

 make the many and rapid 

 changes of coloration take place 

 and it is influenced by two ex- 

 ternal factors and two internal 

 elements. 



The function of this factor is to 

 supply both the quality and 

 quantity of the various pig- 

 ments producing coloration. 



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