GRILSE 43 



its native element." The exhaustive and most im- 

 portant investigations of Dr. Noel Paton and his 

 colleagues demonstrated most clearly the manner, 

 inter alia, in which the great store of nourishment 

 is used up in the development of the genitalia, and 

 showed the corresponding loss in muscular tissue as 

 this development proceeds. With the condition of 

 satiety comes naturally the disposition to cease feed- 

 ing, and with the cessation of feeding the ascent of 

 fresh water commonly follows. 



So far we seem to be on perfectly safe ground, 

 but I am inclined to think that the condition of 

 satiety has been somewhat forced in the argument 

 as to the result which it produces, viz., the ascent of 

 fresh water. I admit that the normal condition of 

 fish on entering fresh water is that of high nutrition, 

 but let us inquire a little further into the argument 

 that this hiarh state of nutrition causes the salmon 

 to leave the sea for the fresh water, or at any rate 

 that this is the primary and dominating factor in 

 the migration. Being in this highly fed up state, 

 fish are able to fast for long periods ; and be it noted 

 this is not peculiar to the salmon, but has been 

 ascertained to be true, for instance, in the allied 

 herring, whilst amongst higher animals the same 

 peculiarity is reported as being true of seals. Why 

 do they fast, and why does the salmon so fast only 

 in fresh water ? It has been said by way of explana- 

 tion that, having attained an overplus of nutriment 

 in its tissues, the salmon enters fresh water to rest, 

 and that this may be regarded as natural, since in 

 entering fresh water the salmon is in reality, as it 



