210 SPECIES IN OUR SALMONIDAE 



common ancestor, a conclusion leading to the 

 difficult and much disputed question whether 

 this common progenitor was of marine or fresh 

 water origin. On this point opinion has always 

 varied. Dr. Day, while not committing himself 

 to a decided pronouncement, appears to incline 

 to the view of a marine ancestry, and such is 

 also the opinion of that eminent authority, Mr. 

 Calderwood. One hesitates to oppose views of 

 such weight ; yet we are met with the fact that 

 all of our salmones are only capable of reproduc- 

 tion in fresh water. It is well established that 

 even in slightly brackish water their ova lose 

 vitality and perish at once. 



In the case of our migratory birds we find 

 the homing instinct urging them, as the season 

 of reproduction approaches, to seek the furthest 

 limits of their migration, ever pressing in face 

 of all difficulties towards those northern regions 

 that are held to have been the place of origin 

 of their ancestors. It would seem, then, some- 

 what strange to find, in the case of the Sal- 

 monidae, this homing instinct not only lost but 

 absolutely reversed. A point rather in favour 

 of the other contention should, however, be 

 mentioned. Certain small streams and chains 

 of lochans in the north of Scotland were, a 

 number of years ago, full of small trout in their 



