52 SCIENCE SKETCHES. 



development of the organs of generation. High 

 water on any of these rivers in the spring is always 

 followed by an increased run of salmon. The 

 salmon-canners think — and this is probably true — 

 that salmon which would not have run till later 

 are brought up by the contact with the cold water. 

 The cause of this effect of cold fresh water is not 

 understood. We may call it an instinct of the 

 salmon, which is another way of expressing our 

 ignorance. In general, it seems to be true that in 

 those rivers and during those years when the 

 spring run is greatest, the fall run is least to be 

 depended on. 



As the season advances, smaller and younger 

 salmon of these species (quinnat and blue-back) 

 enter the rivers to spawn, and in the fall these 

 young specimens are very numerous. We have 

 thus far failed to notice any gradations in size or 

 appearance of these young fish by which their 

 ages could be ascertained. It is, however, prob- 

 able that some of both sexes reproduce at the age 

 of one year. In Frazer River, in the fall, quinnat 

 male grilse of every size, from eight inches up- 

 wards, were running, the milt fully developed, but 

 usually not showing the hooked jaws and dark 

 colors of the older males. Females less than eigh- 

 teen inches in length were rare. All of either 

 sex, large and small, then in the river, had the 

 ovaries or milt developed. Little blue-backs of 

 every size, down to six inches, are also found in 

 the upper Columbia in the fall, with their organs 

 of generation fully developed. Nineteen twentieths 

 of these young fish are males, and some of them 



