SALMONID^. 641 



appear to stray so far away from their native place as to be 

 unable to tind their way back. Almost every year Salmon 

 and Sea-trout in the Grilse-state make their appearance at 

 the mouth of the Thames (where the migrating Salmonoids 

 have become extinct for many years), ready to reascend and 

 to restock this river as soon as its poisoned water shaU. be 

 sufficiently purified to allow them a passage. 



6. There has been much dispute about the time required 

 for the growth of Salmonoids. The numerous and apparently 

 contradictory observations tend to show that there is a great 

 amount of variation even among individuals of the same 

 origin living under the same circumstances, some of them 

 growing much more quickly than others, and being ready 

 to descend to the sea twelve months before their brethren. 

 The cause of this irregularity is not explained. On the other 

 hand, when we consider the fibrous condition of the Sal- 

 monoid skeleton, which is much less solid, and more want- 

 ing in calcareous siibstance, than that of the majority of 

 Teleosteous fishes, we shall be quite prepared to adopt 

 the truth of the observation that the young Salmonoids 

 return to the fresh water, after a few months sojourn in 

 the sea, and after having feasted on nourishing Crustaceans, 

 Sand-eels, etc., with their former weight in ounces increased 

 to pounds. 



7. Liability to variation in form indicates that an animal 

 can adapt itself to a variety of circumstances ; therefore, such 

 species as show the greatest pliability in this respect, are 

 those which most recommend themselves for domestication 

 and acclimatisation within certain climatic limits. Thus, the 

 Eiver-trout or Sea-trout were very proper subjects for those 

 eminently successful attempts to establish them in similar 

 latitudes of the Southern Hemisphere, whilst the attempt of 

 transferring them into the low hill-streams of India ended (as 

 could be foreseen) in a total failure. Those two species must 



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