1 
[mcuurricx] LIFE CYCLES OF THE PACIFIC COAST SALMON D 
The central nucleus (Plate X. fig. 2) is surrounded by the usual 
lines indicating the growth in fresh water and then follows a relatively 
narrow zone of broad lines representing presumably the first summer 
in the sea. Succeeding this zone comes the winter “check,” and follow- 
ing this a zone of broad lines extending to the margin of the scale and 
representing the second summer’s growth. This succession of zones is 
repeated without essential variations in all the fish examined and the 
only distinctive peculiarity, as compared with the arrangement in the 
Coho, is the narrowness of the zone representing the first summer. It 
would seem to indicate an unusually slow growth of the fish during this 
period of its life, a condition for which our present knowledge of the 
life history of the species offers no explanation. It probably is corre- 
lated with the small size of the scales. 
The fact that the scale markings indicate a two year life cycle for 
the Humpback Salmon is of especial interest in connection with the 
belief generally entertained by those engaged in canning operations in 
the Fraser River district that “good” runs of Humpback occur only in 
alternate years. This, if correct, recalls the condition known to obtain 
in the case of the Sockeye of the same district, in which a “good” run 
occurs only every fourth year. The difference might be explained either 
on the supposition that the Humpbacks have a two year cycle and that 
the broods of one of the two year periods are much more abundant than 
those of the other, or else that the life cycle is one of four years, as in 
the case of the Sockeye, but that two of the broods in each quadrennial 
period surpass the other two in abundance. The evidence derived from 
a study of the scales demonstrates that the first of these two supposi- 
tions is the correct one, and this must be taken into account in any 
attempt to explain the periodicity in the runs of fish in the Fraser River 
district. 
THE OToLirus. 
The sagittæ of the Humpback Salmon present an appearance quite 
different from that seen in the other species of Oncorhynchus that have 
been examined. They are, in the first place, decidedly irregular in 
form (Text-figs. 6-8), failing to show the distinctly sagittate form 
characteristic in the other species. This is largely due to irregularities 
in the development of the rostral region, some ossicles having this 
region greatly reduced in size, while in others it is distinct, though 
feeble and irregular in form. The acustic groove is complete in all 
cases and is not interrupted at the constriction (Text-fig. 6). 
But it is in the arrangement of the clear and dark material that the 
greatest difference obtains. Regular zones, such as may be made out in 
the ossicles from other species, either do not occur or are but very 
