254 THE .\JsrGLER-NATUEALIST. 



on tlieir return from it^ some as Grilse and some as spring 

 Salmon, but that it also extends to the old and adult fish 

 after spawning— one portion of these latter coming back 

 into the rivers during the following summer, and the rest 

 not until the spring succeeding it; in other words (and 

 this is the gist of the whole), that at least a proportion of 

 Salmon spawn only every alternate year*. 



The design of this law or instinct — which, when once 

 apprehended, will be found to explain many of the perplexi- 

 ties in the history of the Salmon — is intelligible enough, 

 viz. to ensure a supply of clean fish throughout as large a 

 portion of the year as possible, and to enable each river to 

 support the greatest stock, — a result which could only be 

 obtained by such a provision as the above. It is also 

 doubtless intended to ensure an equal distribution of the 

 fish throughout the whole length of the river. These 

 Salmon, by ascending thus early, before their spawn is at 

 all matured, are vigorous, and able to overcome the ob- 

 stacles in their upward course to the extreme sources 

 of the river — to which those fish which remain in the sea 



* An analogous fact was observed by Dr. Davy with repard to the 

 spawnino; of the common Trout. Dr. Davy was in the habit of open- 

 ing the fish he caught, and by this means he discovered that, as the 

 spawning-season approached, only about one half of the females liad 

 \-i3ible eggs, whilst in the other half there were no sigiu of the develop- 

 ment of the ova. Chan-, also, are frequently taken in Wiudennere in 

 high condition in October and November, which is their regular 

 spawning-season, — a fact which would seem to point to the possibilit-^- 

 of the rule of alternate spawning-years holding good in the case of all 

 the fish here included under the genus Saliiio. 



