THE SALMON FAMILY 61 
another like the tiles on the roof of a house, the free 
edge of the scales being towards the tail. The number 
of scales on any particular fish remains the same through- 
out life, and as the fish grows in size the scales grow in 
proportion so as to cover the skin entirely. 
The increase in size of the scales is by the means of 
rings of growth, which are added round the edges, in 
a manner similar to the rings of growth seen in the 
section of the stem of a tree. It is the arrangement of 
these rings of growth that affords an indication of the 
age of a fish. During the summer, when the weather 
is warm and food is plentiful, the fish grows rapidly in 
size, the scale grows at a proportionate rate, and so each 
ring of growth is of considerable width. In the winter 
the growth of the fish is retarded, and so each ring of 
growth is narrow. 
The outer edge of each ring of growth is marked by 
a distinct line. The summer growth on a scale is seen 
as a broad, light crescentic band, in consequence of these 
lines being far apart, and winter growth is shown as a 
narrow dark crescentic band, in consequence of these 
lines being close together. In this way it is possible 
to read the age of a fish by the arrangement of the rings 
of growth on its scales. 
Calderwood, Johnson, Hutton, Mallock and others 
have thoroughly studied the scales of the salmon, and 
have in this, and in other ways, considerably added to 
our knowledge of its life history. By the scale markings 
it is possible to state when the smolt went to sea, how 
