THE SCALES OF THE SALMONID^ 257 



obliterated up to the central axis of the scale, to a certain 

 extent owing to the physiological changes which are 

 associated with the act of spawning, but principally to 

 the decrepitation which will occur to the exposed surfaces 

 from the trituration of gravel, rocks, etc., while the lesser 

 decrepitation which takes place in the markings situated 

 on other parts of the scale but chiefly in the lateral 

 can only be due to the changed physiological condition 

 of the fish, and to the shrinking of its girth. 



It is probable that the discoloration, if not the direct 

 decrepitation of its scale material, is due to the absence of 

 some element possibly calcareous from the mucous 

 matter which forms and nourishes the scales. 



Whatever may be the cause of its absence, the later 

 formed laminae of the scale material are the ones to 

 suffer, more particularly in the lateral direction. I think 

 we owe to Mr. Calderwood the suggestion that scales must 

 suffer in the hen fish when the body shrinks as the ova 

 of the fish is discharged. Now the fish cannot shrink in 

 its length, but only in its girth, and the fact that the 

 decrepitation principally occurs in the lateral substantiates 

 Mr. Calderwood's theory. 



The decrepitation of the male salmon's scales occurs at 

 a relatively early date to that of the female fish, and con- 

 sequently they become more marked by the end of the 

 season ; this is understandable when it is remembered the 

 different effects which a spawning condition has on the 

 male and female salmon. 



There does not appear to be any unimpeachable evidence 

 that the genital changes produce decrepitation of the scales, 

 or even affect the appearance of the salmon while in the sea. 

 The arousing of the spawning instincts causes the fish to 

 approach our shores, but their appetites appear to be 

 unaltered until they enter the estuaries, or as the winter 



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