64 The Natural History of the Salmon, 



from their native place, as to be unable to find their 

 way back ; almost every year salmon in the grilse 

 state, and sea trout make their appearance at the 

 mouth of the Thames (where the migrating 

 salmonoids have become extinct for many years), 

 ready to re-ascend and re-stock the river as soon as 

 its poisoned water shall be sufficiently purified to 

 allow them a passage.' 



" 6. There has been much dispute about the time 

 required for the growth of salmonoids. The nume- 

 rous and apparently contradictory observations, 

 tend to show that there is a great amount of varia- 

 tion, 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 salmonoid skeleton, which 

 is much less solid and more wanting in calcareous 

 substance than that of the majority of Teleosteous 

 fishes, we shall be quite prepared to adopt the truth 

 of the observations that the young salmonoids 

 return to the fresh water after a few months* sojourn 

 in the sea, and after having feasted on nourishing 



' The Thames for some years past has had a great number 

 of parr put into the upper waters. Are they the grilse and 

 sea trout constantly found at its mouth ? (H.) 



