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formed in the first year are, moreover, very narrow, those of the 
second year are wider; finally, those formed in the beginning of 
that second year can often be distinguished from the rings formed 
later in the same year by a somewhat greater width. 
A part, most probably a very great part, of the two year old 
salmon, with, the majority of the one year old parrs, leave the upper 
course of the Rhine in early spring to reach (in May) the mouth 
of the river in Holland and thence the salt water. There can be no 
question that but a few — like the little fish, the scale of which is 
seen in fig. 13 — remain in the river over two years. It is gener¬ 
ally admitted, however, that these will also find their way eventually 
to the sea. 
c. The young salmon, which are about to enter the sea. 
Some years ago (1896) I had an opportunity of investigating between 
three and four hundred young salmon (smolts), which were caught 
in- May in one of our estuaries and which were on the point of 
arriving at the sea. Regarding the age of these salmon I was only 
able to say *), that the curve drawn for the length of these salmon 
seemed to demonstrate, that they were all of the same age. The 
length of these salmon varied from 11.5—21.3 cm., no less than 
95 % of them, however, were from 12—17.5 cm. A sample was 
preserved in spirits and so it was possible (in 1909) to investigate 
forty specimens as to their age with the aid of their scales. Their 
length was from 12—17.5 cm. Of these 26, length varying from 
12— 16 cm., were upwards of one year old ; and 13, length from 
14.5—17.5 cm., were 'upwards of two years old. That the length 
alone is a bad criterion for the determination of the age is shown 
by the circumstance, that of 19 of these smolts, of from 14.5—16 cm., 
12 were found to be upwards of one year and no less than 7 
upwards of two year old fish. 
The figures 14 and 15 are from the scales of two of these fish. 
They leave no doubt as to their age: the first is from the scale of 
a smolt of 12.6 cm., the age of which, in May, was about 14 
months, the other from a smolt of 16.8 cm., which at the moment 
of the catch was about 26 months old. The first shows the margin, 
which indicates the period of rest in the first winter, and also the 
uot very numerous rings of growth formed since that period; in the 
other specimen the lines indicating the period of rest in both winters 
are easily distinguishable. 
l ) Hoek, Neuere Lachs- und Maifischstudien. Tijdschr. d. Ned. Dierk. Vereen. 
(2). VI. 1899. 
