ON SALMON. 



81 



to how far the sexual organs were developed, i.e., whether the fish would 

 spawn in the following autumn. Disregarding the question of size they are 

 divided in the following table according to their age and the state of the 

 sexual organs. 



UR. Unripe, i.e., sexual organs not matured. 

 R. Ripe or ready to spawn in autumn. 



As the above fish were caught between July and September, it is 

 evident that the age when migration would take place would have to be 

 increased by another winter, as they must spend another winter in the 

 river before they could migrate as smolts in the following May or June. 



As regards the relative proportion of fish of different ages the table 

 cannot give any conclusive evidence, since all the fish were caught either 

 with fly or hook. For that reason the smallest class of fish would not be so 

 fairly represented as the older and larger fish. In most places it is 

 impossible to catch the fish in any other way. The same objection applies 

 also to drawing any conclusions as to the relative size of the various ages, 

 which one can, however, study with the help of the tables in the appendix. 

 Our table shows us two things clearly. 



First, we must note a very distinct tendency for the fish to remain 

 longer in the river in the northern regions than further south. We have 

 further confirmation of this, as will be seen later from the other tables. 



Secondly, on investigating the sexual organs we find a remarkable 

 circumstance. The female fish were all without ova, but of the males a not 

 inconsiderable number were ripe. From the swollen milt it was evident 

 that many of these would spawn in the ensuing autumn. 



That these small male fish were really ripe was confirmed by examining 



similar male fish in the late autumn. They then had free running milt, 



which on microscopic examination was found to contain living spermatozoa. 



The table also shows clearly in what proportion the sexually developed 



male fish are distributed among the various year-classes. 



We see that in the Oselv there was only one ripe male among the fish 

 which had completed their first winter, whereas among the two-winters fish 



