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 
