PREFACE 



Ihe present paper comes as a natural conclusion to the studies on the early stages 

 of the common Atlantic gadoids with which I have been engaged for several years through 

 the investigations of our Danish research-steamer "Thor". These studies have chiefly had 

 a systematic direction hitherto, as it was first of all of importance to obtain a somewhat 

 broader systematic basis, before the biological side of the investigations could be submitted 

 to a comprehensive and general treatment. 



It was not without great misgivings, as will be understood, that I have ventured 

 to include in this work the portion of the Atlantic waters lying off the British Isles 

 and Prance, which I have relatively little investigated, and to connect the results from 

 these waters with those from the most northern parts of the Atlantic, Iceland and the 

 Faeroes, really my own sphere of work and with the conditions of which I was best 

 acquainted. That I have thus to some extent overstepped the boundaries of my own 

 sphere is at one and the same time the weakness and strength of the present work — 

 the weakness because my available material from these more southern waters has not in 

 several cases been quite satisfactory, and the strength since many of the species could 

 thus be studied not only at the northern boundary of their occurrence but also at the 

 southern, which naturally gives a greater certainty to our judgment of the outer factors 

 which determine where spawning takes place and the distribution as a whole. To solve 

 these problems, to endeavour from more vague and uncertain pictures to reach more defi- 

 nite knowledge regarding the conditions which determine that a species spawns here and 

 not there, occurs here and not there, in short to understand the geography of the species, 

 has been the main aim of my present work apart from the establishment of some new 

 facts. 1 certainly recognise that after all I have only been able to give quite a rough out- 

 line of what is necessary for such precision, and I have no doubt that much of my data 

 here will prove as our knowledge gradually advances to be both defective and even to 

 contain some errors. Nevertheless the end will be attained for me in the main, if future 

 investigators can build upon this work as a basis. Further, the Charts and lists contain- 

 ing the records of our hauls in the different waters will remain as quite objective mate- 

 rial which all who may in future be engaged in the study of these conditions and problems 

 will be able to utilize in forming their own conclusions. I have therefore specially wished 

 to publish in extenso these detailed tables which contain a vast amount of labour, as in 

 all probability it will be a long time before a research-vessel will have the opportunity to 

 make so many, quite uniform hauls in such different regions as the "Thor" has had during 

 the years 1903—1907. 



