age at maturity of the pacific coast salmon 
17 
examined than any to which we have had access in search of 4-year-old individuals, 
but such may not be found. 
Experimental evidence is thus far largely lacking in Pacific salmon to corroborate 
inferences we draw from scale structure. But in the coho we have one piece of evidence 
conclusive as far as it goes. In the midwinter of 1910-11, with the assistance of 
Superintendent Frank A. Shebley and Mr. W. H. Rich, we marked a certain number 
of yearlings in Scotts Creek, Santa Cruz County, Cal., by excising both ventral fins. In 
the spawning run of the winter of 1911-12 several of these returned to the same stream 
as mature male grilse, with scales clearly in agreement with their known age, having 
formed a single summer band outside the close-ringed nuclear area and a marginal 
narrowing for the fall growth. Full-grown fish differ from these only in having com- 
pleted the winter band and one additional summer band. A more detailed account of 
this experiment will be given later. 
Prof. McMurrich announces the coho adult to be 2 years old. He has here again 
underestimated by one year the significance of the nuclear area. 
DOG SALMON (Oncorhynchus keta). 
[PI. xm; fig. 26, pi. XIV; pi. xv and xvi.] 
Less is known of the life history of the dog salmon than of any of the species thus 
far considered. Our knowledge of the young is entirely due to Chamberlain, who 
secured them on their seaward migration as fry, some with remnants of the yolk still 
attached. They were not associated with larger individuals which could be considered 
yearlings. As stated by Chamberlain, “records of the occurrence of larger individuals 
in streams have not been authenticated, and, so far as known, all leave the fresh water 
as soon as they are able to swim.” Records of yearling dog salmon have been made 
by the writer and by others in the streams of Washington, Oregon, and California, but 
all such have been founded on incorrect identification of the coho yearlings. 
At the time of the seaward migration of the fry no scales have been formed. It is 
therefore obvious that even the inner rings of the nuclear area give the history of life 
in the sea and not in the fresh water. 
In late April, 1911, we found the fry of this species about 1^2 inches long, very 
numerous about the wharves and shores at Seattle, vigorously feeding on ostracods to 
the exclusion of other food. In midsummer, fingerlings are to be seen abundantly in 
the Puget Sound traps. In common with the young of other species they pass along 
the lead and into the heart of the trap, where they remain until forced to pass through 
the coarse meshes of the webbing. 
The fingerlings of the dog salmon are then conspicuous among the others by their 
slender, graceful form, the dark blue of the back and the conspicuous black margins of 
the tail. Plate xm, figure 23, represents the scale of such a specimen, 6 inches long, 
taken August 2, 1909, from a trap in the Gulf of Georgia. It will be noted that the rings 
are widely spaced, indicating much more vigorous growth than is commonly shown by 
such young of other species as spend their first summer in fresh water. The rings are 
