THE SALT-WATER FISHERIES OF BOHUSLAN. 219 



a. Some deny the occurrence of more than one race of herrings in 

 one and. the same phxce, the difference between coast-lierring and 

 sea-herrings (littoral and iielagiau herrings) and regular migra- 

 tions {G. 0. Sars). 



b. Others maintain that there is a relative difference between coast- 

 herrings and sea-herrings, that more than one race of herrings 

 may be found in one and the same place, and that the great 

 schools of herrings migrate regulai-ly {A. V. Ljungman). ^ 



68. It is doubtless necessary from time to time to give a review of the 

 results of the scientific investigations, so as to obtain a suitable starting- 

 point for new and systematic researches. As the scientific material has 

 been considerably increased during the seven years since Axel Boeck 

 published his well-known work '' Om Silden og Sildefislierierne" (The 

 herring and the herring-fisheries), a new review of this material had be- 

 come necessary to show the extent and character of our present knowl- 

 edge, and to present the different opinions on a subject of such vast 

 economical importance as the herring-fisheries. In endeavoring to con- 

 tribute my share towards the solution of this important problem, I have 

 invariably directed attention to the necessar}^ theoretical premises, which, 

 unfortunately, has often been neglected. In doing this one is less ex- 

 posed to the danger of being led astray by the false hope of having hit 

 the right thing in every case; a clearer view of all the points is gained, 

 as well as a knowledge of the difficulties and of the insufficient charac- 

 teft" of the means by which these difficulties can be overcome. This will 

 make us more humble and more cautious, and help us to avoid the proud 

 certainty which is so often found in older and less critical works. As 

 it cannot be expected that this in itself most difficult and practically 

 most important question regarding a part of the biology of the herrings 

 can be quickly solved by the labor of owe person, it will be necessary 

 that naturalists who have given attention to this subject should freely 

 communicate to each other their different theories and the results of 

 their investigations. The historic review of these investigations shows 

 how beneficial and indispensable this interchange of ideas has been. 

 The mere gathering of facts does not lead to any great result. These 

 facts must be compared and combined into more or less developed theo- 

 ries, always, of course, remembering that there is a chance of these theories 

 leading to no results or only to partial results. Theories are frequently 

 apt to mislead ; but even from the most erroneous theories some useful 

 truth may finally be developed by constant work and by a continued 

 purifying and eliminating process. Mistakes play an important part in 

 the development of human knowledge and lead to greater caution and 

 thoughtfulness in the future. The very knowledge that something is 

 not as we supposed at first, is a step forward ; in order that an erro- 

 neous opinion may be refuted, such an opinion must first have been ad- 

 vanced. My opinion on this point may also serve as an explanation of 

 the circumstance that both in this and in former articles I have given 



