( 488 ) 
thp scales placed above and in front of it, the anterior part being 
totally covered by the adjoining scales 1 ). Lines running parallel to 
its circumference are seen on the exterior surface of the scale; they 
can easily be made out (even when only a weak magnifying power 
is used) on the anterior concealed part of the scale and are indistinct 
or wanting on its posterior area. By developing these lines which are 
really ridges, the outer surface becomes rough like that of a minute 
file, and this we can feel when going over it with a needle *). These 
ridges represent so many stages in the growth of the scale. Why 
it is that the scales do not grow continuously, so to say quite 
regularly, I do not know; in fact the impression we have of the 
growth is, that in the course of a year a certain number, 12, 15, 
20 new growths, like so many rings, are added to the circumference 
of the scale and that each growth, in the shape of a delicate ridge, 
leaves a lasting token on the surface. If the growth takes place more 
rapidly, then the number of ridges added in the same period is 
larger; moreover the width of the rings, which is to be judged from 
the distance of the ridges, increases with the age of the fishes. 
If the growth of the scale took place quite 'equally or even with a 
gradually increasing rate the whole year round, the growth-ridges 
of the outer surface would not give us better information, with 
regard to the age of the fishes than the growth of the scale itself 
would afford. In that case we should only be able to say: larger 
fishes have larger scales, larger scales have more numerous lines of 
growth and when approaching the outer Circumference these lines are 
more distant from one another than those of the central part. As, 
however, the number of rings, formed annually is found to be very 
unstable, it would be impossible in that case to draw conclusions 
regarding the age of the scale (and the fish itself in general) from 
the structure of that scale. That this is indeed possible is caused by 
the following: 
1 st . because the young salmon, living' in fresh water does not 
take any food during a certain period in wintertime, and does not 
grow; in that period the scale does not grow either; when afterwards 
the same fish begins to grow again, this happens with somewhat 
x ) Anatomically this sketch is not quite exact as each scale (as is well-known) 
lies concealed in a pocket of the skin, from which only the posterior part 
emerges. Moreover these posterior parts, which together form the surface o t e 
body, are covered by a continuous layer of pigment-bearing mucous epiderm-ce 
2 ) As everybody, who is accustomed to manipulate fresh fish knows, scales 
easily get loose from the surface and would no doubt do so still more gu 1 * 
if their surface was smooth on both sides. 
