[mcmurricx] LIFE CYCLES OF THE PACIFIC COAST SALMON 13 
Following upon this comes a second zone of broad lines succeeded 
by a third zone of narrow lines, the two together representing the second 
year spent in the sea, and beyond these there is again a zone of broad 
lines followed by a fourth zone of narrow lines representing the third 
year in the sea. Finally a narrow zone consisting of only a small number 
of broad lines represents the fourth summer in the sea, during which the 
fish was caught on its way to the spawning grounds in fresh water. 
The story told by the scales is then in perfect accord with that de- 
duced from what is known as to the early life of the fish and from the 
evidence furnished by the cannery statistics. The life cycle is one of 
four years; the first winter is spent in fresh water, three summers and 
three winters are spent in the ocean and the fish return to the spawning 
grounds in the fourth summer. In eight out of the ten fish examined, this 
is the story told by the scales markings with a distinctness that is most 
striking. These eight fish measured in length respectively 69.5 cm., 
67 cm., 69 cm., 68 em., 63 cm., and 67 em. In two other fish, how- 
ever slight departures from the typical arrangement of the lines was 
observed. In one, a fish measuring 68.5 em., (Plate II) there were 
four zones of narrow lines in addition to that representing the period 
spent in fresh water, suggesting the possibility that the fish spent four 
years in the sea, instead of three, returning to spawn in its fifth summer. 
Another interpretation seems, however, to be preferable. The second 
zone of narrow lines occurs at about the same distance from the nucleus 
as the first zone in the typical cases and may be supposed to be due to 
the same cause, the slow growth during the first winter spent in the sea. 
The first zone of narrow lines, which falls in a region of the scale typically 
occupied by the broad lines of the first summer’s growth, is probably 
due to a check in growth during the first summer. It may be supposed 
that immediately after reaching the sea the growth was rapid, as in 
typical cases, but later on in the summer in some way the conditions 
became unfavourable and growth was markedly checked; later still the 
fish again found itself in favourable conditions and its rapid growth 
was resumed, continuing until the winter check produced another zone 
of narrow lines. This explanation of the additional narrow zone seems 
preferable to one that demands the addition of a year to the life cycle, 
and receives support from what has been observed in the scales of cer- 
tain Spring Salmon, to be described later on and in connection with 
which a suggestion as to the cause of the “check” will be made. 
In the other departure from the type (Plate III), which occurred in 
a fish also measuring 68.5 c.m. in length, only two zones of narrow 
lines that could be certainly ascribed to winter checks were to be seen 
on the scales. In typical cases the lines representing the growth in fresh 
water cease rather abruptly and are somewhere in the neighbourhood 
Sec. IV., 1912. 2. 
