8 JOHAN HJORT. M.-N. Kl. 



(luced sexual organs. In 1872, Sars^ propouned the very fortunate idea, 

 that the Spring Herring and Summer Herring (the Fat Herring), are but 

 different developments of a like species, or in fact the same individuals. 



Sars thus taught us that the very same mass of herrings makes two 

 important and different migrations towards the coast, the one with the 

 object of spawning (»The Spawning Migration«}, the other in order to 

 seek food '»The Sustenance IMigration«;, and, furthermore, taught us to 

 know the resorts of the herring during the greater part of the year. In 

 the main, he succeeded in giving us an insight into the advances which 

 our principal kinds of fish make towards our shores, and let us under- 

 stand the importance that these influxions have on the cycle of life of 

 the fish. 



But the old experience that the migration of fishes, the intluxions, 

 varies so from year to year, has, however, proved to present by far 

 more complicated problems. 



On the strength of his historical studies A. Boeck- put forward his 

 well known h3'pothesis of the Herring Periods. From historical studies, 

 especially of the Bohuslän's Fishery and the Spring Herring Fisher}-, he 

 thought that he could come to the conclusion that the varying of 

 the influx of the Herrings during one period of years has been great, 

 whilst in the following series of years it has ceased to a greater or lesser 

 extent. He did not, however, succeed in discovering any reason for the 

 difference between these periods, nothwithstanding that we find many 

 hints, and thoughts of great value in his works. 



It will, likewise, be understood, how excessively difficult a matter it 

 must have been for scientific men to get a nearer insight into these ques- 

 tions, when it is remembered how very little the waters off our coasts 

 were then investigated. But very little was known of the conditions of 

 the bottom of the great Northern Ocean, and still less of its physical 

 qualities. 



It is, therefore, not tüfficult to perceive that the migration of fishes in 

 this unknown sea must have been but little known. 



In the years 1876, 1877 and 1878, The Norwegian Northern Ocean 

 Expedition was, however, started, during which the seas off our coast were 

 very thoroughly examined. 



The sea between the Coast of Norwa}^ Jan Mayen, Iceland, the Farø-e 

 Islands, and Scotland forms a deep basin, which, at the deepest point, is 



1 Report for 1872. 



2 Loc. cit. 



