FISHERY PROBLEMS 167 



the same as that of the Dutch sea-coast ; the Dogger 

 herring is of a special race. In the North Sea alone 

 there are three or four distinct races of autumn x herring, 

 and as many of spring herring. The races do not mingle. 

 The herring of one region never show themselves in 

 another region at all events, not in the form of shoals. 

 In the Channel adult herring are taken now and then 

 from the bottom, with the trawl, at all seasons of the 

 year. In summer they are sometimes taken together 

 with mackerel. Three years ago, in the month of 

 October, the fishermen of Boulogne surprised hundreds 

 of thousands of herring in the estuary of the Thames. 

 Mackerel are perhaps even more narrowly localised than 

 herring. The American races differ from the European 

 races. The Irish mackerel differs from that of Plymouth. 

 It is the same with the sardine, the cod, and with flat- 

 fish. In short, direct observation and experiments with 

 marked fish prove the law already enunciated, that the 

 seas are divided into an infinite number of provinces, 

 each provided with its own population, and that a species 

 never leaves the confines of its proper habitat, keeping to 

 its own quarter somewhat as the dogs of Constantinople 

 used to do. 



The history of the earth, in this connection, comes to 

 the aid of oceanography ; thereby only paying a just 

 debt, for in many instances the oceanography of to-day 

 explains the geology of the morrow. The two shores 

 of the Isthmus of Panama, formerly a strait, nourish 

 the same fish ; 30 per cent, are species common to 

 either side. The fish of the Ligurian coast and those 

 of Corsica, Sardinia, and western Italy are the same, 

 because the African continent formerly projected far into 

 the north. On the other hand, there is no such similarity 

 1 Herring spawning in autumn. 



