SPECKLED TROUT. 119 



food, and grew, like all his kind under similar 

 circumstances, to an extraordinary size. Thus 

 he attains, as it were, to a second and final 

 maturity. But salmon cannot lay their eggs 

 in the sea ; or at least, if they did, the young 

 parr would starve for want of their proper 

 food, or else be choked by the salt water, to 

 which the old fish have acclimatised them- 

 selves. Accordingly, with the return of the 

 spawning season there comes back an in- 

 stinctive desire to seek once more the native 

 fresh water. So the salmon return up stream 

 to spawn, and the young are hatched in the 

 kind of surroundings which best suit their 

 tender gills. This instinctive longing for the 

 old home may probably have arisen during 

 an intermediate stage, when the developing 

 species still haunted only the brackish water 

 near the river mouths ; and as those fish alone 

 which returned to the head waters could pre- 

 serve their race, it would soon grow hardened 

 into a habit engrained in the nervous system, 

 like the migration of birds or the clustering 



