408 1p, dg ZNIDIETOING. 
Fig. 3 is from a drawing of the scale of a coal-fish (Gadus virens). The 
surface of the scale appears covered with a series of concentric rings or 
ridges. When growth is proceeding rapidly there is a considerable space 
between succeeding ridges, when growth becomes slow the ridges crowd 
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Fic. 3.—Seale of Coal-fish (Gadus virens). (After Damas.) 
closely together. But the fish grows most rapidly during the summer 
months, when the water is warm and food is plentiful, whereas durmg 
the winter growth becomes slower and slower, and even ceases altogether. 
It is during this winter period of very slow growth that the concentric 
ridges on the scale become crowded together and give the appearance 
of a darker ring on the surface of the scale. On the scale figured there are 
two such winter rings and the growth of the third summer is well advanced. 
That this explanation of the appearance presented by the scale is the 
correct one has been proved by the examination of scales taken from 
fish caught at different times of the year. A fish captured in summer, 
such as the one illustrated, has the ridges far apart at the margin of the 
scale, whilst in fishes captured as the season advances towards winter the 
ridges round the margin become crowded together. 
In the case of the Cod family these markings on the scale are especially 
distinct and the examination of a few scales is generally sufficient to fix 
the age (Winge, 25). The number of winter rings formed by the crowding 
together of the ridges tell us at once the number of years of life which the 
fish has completed. It must be remarked, however, that the appearance 
of these winter rings is not in the case of each individual fish as clear and 
definite as that shown by the scale illustrated, and in a large batch of 
fish a certain number will be doubtful and the exact age a little uncertain, 
