Mitchell has given many sound arguments in refutation of it. He divides the theories upon the subject into three:--first, that the herrings come from the North Pole in great shoals of many leagues in extent, dividing into lesser shoals on coming towards the north point of Scotland; second, that they do not come from the Arctic regions, but from a less northerly direction, still, however, very far north of Shetland; and, third, that they are spawned on the coasts near which they are caught, and are consequently natives; that after spawning, they retire out to sea, and continue so until their spawning season comes round again, when they return to their accustomed shore. The latter he considers to be the most reasonable theory, and adduces in support of it the well-known fact that the herrings at every fishing station are of a peculiar quality uniformly the same, and always different from those at other even very nearly adjoining stations; and so well has this fact been established, that practical men can at once pronounce from the size, appearance, and quality of the fish, where it was taken. For example, the herrings taken off the coast of Stadtland in Norway are almost twice the size of those taken near Shetland, and these are twice the size of those caught near Thurso, whilst the Dublin Bay herrings have long been famous for their superior flavour, which is unmatched by those of any other bay or harbour. Again, a size of herrings similar to those of Yarmouth visited till lately the coast of Lumfiord in Denmark, whilst on the Mecklenburg coast higher up the Baltic, the herrings are one-third larger than those of Lumfiord; and proceeding up the Baltic above Mecklenburg to the Pomeranian and part of the Prussian coasts, they are fully one-third _smaller_; and again still farther up they are larger. In quality and condition they differ as much as in size, those off the coast of Holland being so inferior as not to be worth pickling, and the Dutch fishermen consequently seek the coasts of Scotland and England. As to the time of appearance at the several fishing stations, their irregularity goes far to prove their constant propinquity, the take commencing at some of the more southern stations before the northern ones; whereas, if they migrated regularly from the north, it is evident that the fishing should commence at the various stations in regular order, from the most northern where the shoals would first make their appearance, to the next, and so on to the most southward, which should be deserted by them at some certain season, in order that they might return.