of the Salmon in Fresh Water. 



doubt, but, so far as I am aware, there is absolutely no evidence that once 

 having fairly pntered the river they ever return to the sea in any con- 

 siderable number. Were this the case, did a constant to-and-fro migra- 

 tion from sea to river and river to sea occur, we should not expect to find 

 any marked difference between the fish in the estuaries and the fish in 

 the upper reaches. But our figures show that as regards weight, as 

 regards weight of muscle, and as regards weight of ovaries and testes, 

 there is a mai-ked difference, becoming more accentuated as the season 

 advances, between fish in estuary and fish in the upper waters. And 

 the more carefully these figures are analysed the more forcibly do they 

 tell against such a to-and-fro movement. 



In considering the total weight of the salmon, it might be thought 

 that the very marked overlap between the heaviest fish in the upper 

 reaches and the lightest fish in the estuary favoured this view. 



Weight per Standard Fish. 



Analyses of the weights of the musculature and of the ovaries shows 

 that no significance can be given to these figures. ^ 1 



In the first place the very small overlap between the smallest ovaries 

 of the upper-water fish and the largest ovaries of the estuary fish 

 opposes the idea of there being any free exchange between these 

 situations. 



Weight of Ovaries per Standard Fish. 



But a comparison of the musculature is the most convincing. In May 

 and June while the fish are running, when no time has been allowed for 

 any difference to develop between the fish leaving the sea and those in 

 the upper reaches, the overlap between the largest musculature of the 

 upper-water fish and the smallest musculature of the estuary fish is 

 fairly marked. By July and August the overlap has practically ceased 

 to exist, and by October and November the heaviest musculature of the 

 upper-water fish is less than the smallest musculature of the estuary 

 fish. 



