[mcmurRicH] LIFE CYCLES OF THE PACIFIC COAST SALMON 5 
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“I 
The natural interpretation of these appearances is that the dark 
areas represent the older portions of the ossicle and the clear ones the 
portions that have been recently added.’ But the marked variation in 
the relative amount and distribution of the two substances indicates that 
the conditions are by no means so simple as such a bare statement 
would imply. The appearances presented rather suggest resorption of 
material and attempts at regeneration. Such an ossicle as that shown 
in Text-figure 8 suggests the probability that at one time it had pre- 
sented a form and structure essentially similar to those seen in the other 
species of Oncorhynchus, and that later there had been an extensive 
resorption of a portion of the ossicle, with a subsequent attempt at 
regeneration. And the same interpretation would serve for the other 
ossicles figured, the only difference being that in these the resorption 
had been somewhat more extensive. 
But in what manner this process is correlated with peculiarities in 
the life history of the species it is impossible to say at present. This 
and the narrowness of the zone in the scales representing the first 
summer’s growth are distinctive of the Humpback, and both seem to 
indicate peculiarities in its life history. The two, apparently, do not 
stand in correlation, since, from the fact that a faint clear line can 
frequently be detected in the otoliths in the region where the winter 
“check” should be expected, it would appear that the resorption and 
regeneration of the ossicle was a phenomenon occuring during the 
second summer. It would be interesting to determine whether it was 
related to the marked structural changes which accompany sexual 
maturity. 
As might be expected the size of the sagitta of the Humpback 
Salmon falls below that of the other species. In the six individuals 
examined its length and breadth were respectively 3.5 and 2.5 mm., 
3.5 and 2.5 mm., 3.75 and 2.5 mm., 3.5 and 2.5 mm., 4.0 and 2.5 mm., 
3.5 and 2.5 mm. 
SUMMARY. 
The more important results of this study may be briefly sum- 
marized as follows :— 
1. According to the length of their life cycle the species of 
Oncorhynchus occurring on the West Coast may be divided into two 
groups, one, including the Sockeye (O. nerka), the Spring Salmon 
(O. tschawytscha) and the Dog Salmon (O. keta), in which the cycle 
extends through four years, and a second, including the Coho (0. 
kisutch) and the Humpback (0. gorbuscha), in which the cycle is limited 
to two years. 
