MIGRATION. 165 



found in the Severn, into a more southern 

 latitude than ordinary, from whence they made 

 their way to that neighbourhood." The ap- 

 pearance of the harp seal in our seas is merely 

 accidental ; it has been shot near the Orkney 

 Islands. The probability is, that all seals are 

 more or less migratory. The elephant seal 

 (Phoca jwoboscidia) of the Southern Ocean, 

 according to the best information which we 

 possess, travels between latitude 35° and 50°, 

 passing to the Antarctic in summer, and retrac- 

 ing its course in winter. 



It has been asserted by many that fishes 

 perform extensive migrations ; but perhaps 

 it will be found that their migratory journeys, 

 though regular, are far more limited than has 

 been supposed. For example, the mackerel 

 was believed by Anderson, Duhamel, and 

 others, to be a fish of passage, performing, like 

 some birds, certain periodical migrations, and 

 making long voyages from north to south at 

 one season of the year, and the reverse at 

 another. Mr. Yarrell combats this error, ob- 

 serving — " It does not appear to have been 

 sufficiently considered, that inhabiting a medium 

 which varies but little either in its temperature 

 or production, locally, fishes are removed be- 

 yond the influence of the two principal causes 

 which make temporary change of situation 

 necessary. Independently of the difficulty of 

 tracing the course pursued through so vast an 

 expanse of water, the order of the appearance 

 of the fish at different places on the temperate 



