NATURAL HISTORY OF THE SALMON. 49 



perature of the ponds, as compared with that of the 

 river, was on one occasion three degrees below, and on 

 another six degrees above. So whatever difference there 

 was, seems to have been in favour of the pond stimulat- 

 ing, not retarding, as compared with the river or natural 

 habitat. But suppose it were otherwise, what then ? 

 We know that a lower temperature might retard the 

 hatching of the fry by a week or two, or their growth 

 by half an inch or half an ounce ; but we have no 

 ground for supposing that it would retard for a whole 

 year such a change as that of assuming the migratory 

 dress — ^taking place, as that does, at a fixed season of 

 each year — especially as the fact of that change not 

 being dependent on size, development, or condition, is 

 evidenced by the great difference in all these respects 

 observable among the descending smolts. Again, on the 

 one hand, it has been argued that the young fish at Stor- 

 montfield were probably not sufficiently fed, else they 

 might all have arrived at the migratory stage the first 

 year ; but it is also said, and with fully as much show of 

 reason, that as the fish were regularly fed with " boUed 

 liver rubbed small," besides their natural supplies from 

 the surface and the bottom, it is supposable that but for 

 that none of them would have developed the migratory 

 instinct until the second year. StiU further, it is said 

 that if the fish had been in the open river, subject to the 

 influences of floods, they would have descended the first 

 year ; but yet again it is replied, and with at least 

 equal show of reason, that if the fish had not been led, 

 or encouraged, or almost driven out of the ponds, none 

 of them would have removed the first year. 



