09 
stages were concerned, but proved unreliable in the case ol the older fish, exactly as 
we have seen in Chap. | when dealing with herring, the older year classes melting one 
into another without any distinct limit between (vide Chap. I, Figs. 5—7). Not until the 
introduction of the method of studying otoliths, bones, and scales was it found possible 
to arrive at accurate determinations of age for the individual fish, and thus obtain reli- 
able information as to the general composition in point of age. 
Damas’ scale investigations. 
The first extensive investigations based on examination of the scales of the cod 
were carried out by Dr. Damas*), who gives a detailed description of the progress of 
the method. Damas describes the scale of the cod as follows: “The scale of the gadoids, 
when strongly magnified, is found to be composed of polygonal elements, which may 
N 
NAS 
\ 
\\ 
Fig. 78. Scale of a coalfish, 21} years old and 30 cm. long, taken in Nordland, 1907. 
be styled, in the termmology applied to the structure of trees, as cells. In order to avoid 
any erroneous idea as to the morphological value of these, we may call them small poly- 
gonal plates (“plaquettes polygonales”). They are arranged in rows, at once radially 
and concentrically situated, in more or less regular design, each having a sharp edge. 
This gives rise to a number of concentric edges, the plates being divided by radial and 
concentric furrows”. 
From Fig. 78 it will be seen that the size of these small plates varies greatly. The 
innermost ones are large, but soon become highly compressed, then suddenly widening 
out again. Between the most contracted plates and the adjacent larger ones, a sharply 
defined line is seen. The resulting formation is a series of alternating zones of broad 
and narrow plates: the figure shows three of the former and two of the latter. Exami- 
nation of the scales at different times of the year has revealed the fact that the large 
plates are formed in summer, the narrow in winter. According to Stuart THOMPSON, 
*) loc, cit, 
