INTRODUCTORY 21 



agree that there are no known structural differences sufficiently 

 pronounced to warrant the placing of sea-trout and trout in distinct 

 categories. 



2. — The Young of Sea-trout and Trout are Indistinguishable. 



Mr. Regan does not here clearly indicate what he means by " the 

 young," whether eggs, alevins, fry, parr, or smolts, or all or any of 

 them; and if he means indistinguishable in structure I must repeat that 

 I am not in a position to question his accuracy. But if he means in 

 other and more superficial respects — which I assume he does not mean — 

 his statement is too sweeping. I shall later, when discussing each 

 stage in the life-history of the sea-trout, indicate various points wherein 

 I have observed apparently characteristic differences between the 

 young, in all stages, of migratory sea-trout and, presumably, non- 

 migratory trout. Indeed, as I shall show later, it is rather in the mature 

 state that sea-trout and trout tend to become " indistinguishable." But 

 at any rate, as to the young, failing proved differences in structure, I 

 would not be disposed to accept variable superficial differences as 

 evidence of distinction of species, or race, as between migratory and 

 non-migratory trout. Here again, therefore, we may accept Mr. Regan 

 as being substantially sound in his views. 



3. — Sea-trout, if prevented from going to the Sea, will Live and 

 Breed in Fresh Water. 



This is very important. It is, of course, the normal habit of sea- 

 trout to live at least temporarily in fresh water and to breed there. It 

 would, in the present inquiry, be necessary to show either (i) that male 

 and female smolts of sea-trout, having ^-been prevented from migrating 

 to the sea, had been so far contented with their fresh-water environment 

 as to thrive there and in due season propagate their species, or (2) that 

 mature fish, having ascended to fresh water and there spawned, had 

 been prevented from returning to the sea and had thereafter spawned 



