264 Mr D. Ellis on the Natural History of the Salmon. 



March and April ; and the fishing there is nearly over by the 

 middle of May *. A similar remark is applicable to the Lee, 

 and other rivers in Ireland ; to the Eden, Severn, and some 

 others in England ; and to the Ness and Thurso in Scotland. 

 This may probably arise from these rivers possessing a higher 

 mean temperature at the season alluded to, the direct operation 

 of heat, in accelerating the developement of the reproductive or- 

 gans being not less marked and striking in the animal, than it is 

 in the vegetable kingdom. 



Section 3. — Of the Migrations of the Salmon betwixt the 

 Rivers and the Sea. 



We have seen, that the brood of the salmon, after a short re- 

 sidence in the sea, return to rivers greatly increased in size. 

 Many practical fishers, those especially connected with river 

 fisheries, contend, that not only the young brood, but the older 

 salmon, always make efforts to revisit their native rivers. That 

 many do so is proved by the facts already stated, of salmon, 

 which, having been marked on going down to the sea, have been 

 afterwards retaken in the same river, and identified : But it is 

 equally certain, that numbers of fish, thus previously marked, 

 have never been retaken in their native rivers, but sometimes in 

 another that adjoins it ; and when we consider, says Dr Flem- 

 ing, the numerous foes which unceasingly persecute the salmon 

 during its abode in the sea, which must necessarily mix the fa- 

 milies or tribes belonging to different estuaries and rivers, it 

 seems difficult to conceive, how, after such intermixture, the 

 breeds of different rivers could again separate and collect into 

 their original groups -(•. The assertion made by several expe- 

 rienced witnesses, that they can discriminate the salmon of dif- 

 ferent rivers by original peculiarities of form, may be met by 

 that of others, equally experienced, Mr Halliday for example, 

 who denies that any such distinction is practicable. That sal- 

 mon, however, do frequently differ considerably in point of form 

 from one another I have repeatedly witnessed, says Dr Flem- 

 ing, by looking at the fish taken at the same place by the same 

 net, and collected together in a boat ; but these variations are 

 not greater than in other species of animals, subject to variations 

 • Keport I. p. 114. T Report II. p. 70. 



