264 A HISTORY OF FISHES 



is to suffer." Some of the earlier accounts credited the Herring 

 with very extensive wanderings, but this was due mainly to 

 the confusion of the different races now known to exist. It 

 has been discovered that the species may be divided into a large 

 number of races, each with its own range of distribution and 

 its own season of spawning. Thus, it is possible to recognise 

 North Sea, Baltic, Norwegian, Icelandic Herring, and so on, 

 and each of these may include forms spawning at various times 

 of the year. Off the British coasts there is scarcely any month 

 in which spawning is not taking place on one or other of the 

 recognised grounds, and a broad distinction may be made 

 between winter-spawning Herrings shedding their eggs close 

 to the shore, and summer Herrings spawning in deeper water. 

 The migrations undertaken by the different races, concerned 

 either with reproduction or with food, vary greatly in extent, 

 and the Norwegian Spring Herring may move from the south- 

 west coasts of Norway as far north as the Barents Sea and back 

 again, whereas some of the races spawning in the Cattegat 

 and the Belt Sea do not leave these waters. The movements of 

 the shoals between the spawning seasons are less understood, 

 but there is reason to suppose that the fish do not move far away 

 from the coast. It is clear that the times when they congregate 

 in dense shoals are those when they may be most easily caught 

 by the drift-nets of the fishermen, and, as a general rule. 

 Herrings may be said to collect together at four periods of their 

 life: as young fish, as mature fish just before spawning, as 

 spawning fish, and as spent fish soon after spawning has occurred. 

 The sea was probably the original home of fishes, and the 

 numerous and diverse forms found to-day in the rivers, streams, 

 lakes, and ponds have been derived from marine ancestors 

 who were driven to leave the sea through stress of competition, 

 and who found in the fresh waters new food supplies, escape 

 from many enemies, and quiet places in which to breed. 

 Many of these pioneer visitors must have become permanent 

 residents in the new habitat, and the changed conditions acting 

 over many generations led to the formation of fresh-water races, 

 and, as time went on, of species distinct from their marine 

 relatives. In course of time these would tend to spread farther 

 and farther inland, and to become more and more modified, 

 until finally there would be whole families or even larger groups 

 composed entirely of fresh-water fishes such as are found at the 

 present time. To-day, almost every order of fishes includes a 

 greater or lesser number of fresh-water representatives, and one 



