52 



Diep aud those of the Zuiderzee and the IJsel; however these 

 are uot sufficieatly important to distinguish the animals from one 

 another as races or varieties. There is no differeuce in size be- 

 tween the fishes of the Zuiderzee and those of the HoUandsch 

 Diep. Whether the sraelfcs of the Zuiderzee difïer from those of 

 the IJsel-river I dare not decide — however, I can hardly think so. 

 As the smelt of the IJsel comes also from the Zuiderzee, at first 

 it looks rather absurd to admit such a difference: the meaning 

 would be, however, whether a difference existed between those 

 smelts which spawn in the Zuiderzee and those individuals who 

 enter the IJsel for that purpose. I do not believe such difierence 

 exists: I admit that out of the same shoals of smelts part of 

 the fishes ascend the river and part spawn in the Zuiderzee itself. 

 The rich catches of smelt-brood in the neighboorhood of the 

 mouth of the IJsel , where the water of that river reduces the 

 salinity of the sea to a minimum, show that those places are to 

 be considered as the spawning places of this fish. 



The herring is the most important fish for the Zuiderzee- 

 fishermen — and so it has been for several centuries. When the 

 lake Flevo changed into the Zuiderzee a herring entered it with 

 the salt water of the Northsea. What kind of herring was it that 

 made its entrance in this sea? 



There is a very remarkable difference between a herring and a 

 herring! Fishermen and dealers in fish know this perfectly well 

 and so does everybody who has eaten herrings with atteutiou. 

 The practical man knows how to distinguish the diö'erent herrings 

 from one another, the scientists, however, experienced great difEculty 

 in defining those differences, the existence of which could not 

 be deuied. Dr. Heincke ') of Oldenburg has the great merit to 

 have hit the point in this matter. He showed that the methods 

 for distinguishing herring-races as hitherto applied were not even 

 sufficiënt to distinguish from one another two difierent species 



1) Heincke, Fr., Die Varietaten des Herings. Jahresber. der Commission z. Unters. 

 der Deutschen Meere. 1878. S. 4i und 1882. S. 1. 



