[Mcuurricx] LIFE CYCLES OF THE PACIFIC COAST SALMON 19 
year shown by the scales of a number of fish of varying sizes, the length 
of each fish being shown by the figures beneath each vertical line. 
Each of these lines represents the length of a scale measured from the 
centre of the nucleus to the margin of the covered portion and on this 
line intervals have been marked off corresponding to the amount of 
growth of the scale during the period spent in fresh water and during 
the three years spent in the sea. For the sake of ready comparison the 
corresponding time intervals have been connected by horizontal lines, 
but it may be pointed out that these lines or curves have no further 
significance, since as will be seen from the diagram the relative lengths 
of the scales as measured do not correspond with the relative lengths of 
the fish. The intervals represent merely the relative amounts of growth 
in the individual fish for the periods selected. 
In the case of the 73.0 em. fish, it will be seen that while the amount 
of growth during the first year in the sea was good, that of the second 
year was considerably less and that of the third year still less. In 
the 76.0 cm. fish, one of whose scales is shown in Plate VII., the growth 
of the second year in the sea was very poor, but this was to a certain 
extent compensated by an unusual growth during the fourth summer. 
In the 80.0 em. individual one sees indications of poor growth during 
the first and second years in the sea, but, on the other hand, there was 
apparently an unusually rapid growth during the third year. It is un- 
necessary to detail the differences in the various fish, the diagram shows 
sufficiently clearly the variations in the amount of growth in different 
years, a lessened growth occuring sometimes in one and sometimes in 
another year and similarly with a good growth. 
These differences are probably attributable to difference in the food 
supply, certain fish finding themselves on poor feeding grounds in one year 
and on better ones in another, others meeting only a fair supply in 
all three years and others again an abundant supply. But in the 
84.0 cm. and 91.5 em. fish a condition obtains which is not found in 
the other fish examined. In the zone representing the growth during 
the first summer in the sea there is interposed in all the scales from 
these fish a band of narrow lines exactly resembling those formed 
during the winter period, and in the 91.5 em. fish a similar band is 
interposed in the zone representing the second summer. Two inter- 
pretations suggest themselves for these bands. They may possibly 
represent a winters growth, so that instead of being four years old 
the S0.0 cm. fish was really five, and the 91.5 em fish six years old, 
or they may merely represent “checks” in growth of the same nature 
as those that produce the winter zones. I rather incline to this latter 
supposition, and if it be the correct explanation it would seem neces- 
sary to assume the existence of two factors modifying the arrange- 
