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widely differing biological characteristics, although belonging to the same 

 species. A true understanding of the migrations of the cod in general is thus 

 only to be arrived at by a comparative study of the differences in race, 

 structure and mode of life, which characterise the shoals of cod from the 

 different parts of the sea. 



For the purpose of such study, however, the herring, being smaller, and 

 as a rule much more numerous in the waters it inhabits, is beyond doubt far 

 more suitable than the cod. We have also the further great advantage with 

 the herring, thas this fish has already repeatedly been made the object of 

 excellent investigations in this respect (cf. the earher work of Nilsson, and 

 later of Heincke). With the study of this, the second migratory fish on the 

 original programme it has been necessary to take the question of race also into 

 consideration. Two more or less detailed reports have already appeared con- 

 cerning these investigations, preliminary studies which deal entirely with the 

 scales of the herring. As is well known, the structure of the scales of various 

 fish has for many years been used as a means of obtaining information con- 

 cerning the age of the fish ; this method has been employed with more or less 

 success to determine the age of carp, several species of the cod family, the 

 pleuronectidœ, the salmon, etc. Also with regard to the herring, the study of 

 scales has been advantageously applied, and this has now, by means of the 

 International Investigations, become possible on a very large scale. Tens of 

 thousands of herrings from the most different fishing grounds, from the Nor- 

 wegian waters and the North Sea, from Iceland, the Faroes, the Shetland Isles, 

 the coasts of Scotland and England, the Zuyder Zee, the Kattegat, etc. 

 have been available for the purpose. The investigations have not been 

 entirely restricted to the determination of age, but have also endeavoured to 

 deal with the question of the possibility of determining what growth has taken 

 place on an average, among the specimens of a certain shoal, during the 

 earlier periods of life at the different seasons of the year ; also how far any 

 relation is to be found between the growth on the one hand and the condition 

 of nourishment of the fish on the other. Endeavours have been made to obtain 

 by this method an exact idea of the composition of a shoal of herrings, and 

 to discover the different ages of the fish of which it consists, and how far they 

 really belong together, etc. 



In spite of the many and careful investigations which have already 

 been made with the herring, yet, as one of the most important, if not the 

 most important of all the North Sea fish, its problems will continue to occupy 

 the attention of scientists as well as fishermen and merchants. The experience 



