THE SCALES OF SALMON 95 



land shark. Moreover, salmon, young and old, 

 small and great, are found with the same number of 

 scales when certain rows are counted, and this 

 character is so constant as to be one of the most 

 trustworthy for the identification of salmon from 

 other species. 



On the other hand, the progressive growth of the 

 scale as viewed in fishes of different age, the increase 

 of size and the definite system upon which this in- 

 crease of size is clearly brought about, the impress 

 of the young condition still visible on the old fish's 

 scale, and the comparison of scales taken at different 

 times from salmon which have been marked and 

 afterwards recaptured, all impress the mind with the 

 conviction that not only does the scale grow as the 

 fish grows, but that the periodic nature of the 

 salmon's growth is stamped upon the scales. 



In early life the scales are merely circular patches 

 on the integument of the post-larval fish. These 

 centres of growth gradually have more and more 

 scale matter added to their peripheries, till inter- 

 vening spaces are all covered and the scales com- 

 mence to overlap. The young salmon is barely two 

 inches long when the growing scales begin to over- 

 lap. The scale matter added to the growing sur- 

 faces appears in a succession of ridges which under 

 the microscope give the appearance of concentric 

 lines round each centre of growth, the whole being 

 covered by a membrane or outer skin. 



By the time the smolt is ready to depart to the sea 

 the overlapping portions of the scales have become 

 less distinct in their line formation than the portion 



