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case that the method, to use the distribution of the plankton eggs and of the earliest, 

 developmental stages (larvae), must contain certain sources of error ; as, for example, that these 

 early stages like all plankton are carried about by the movements of the water-masses. 

 The following section gives numerous examples of this. It results from this, that the 

 spawning regions may often be considered larger than they really are. The richer the 

 material is of the earliest, just hatched stages, the better will the method serve as evidence 

 of the extent of the spawning places. Many observations lead us to conclude that the 

 spavi^ning of most of the species is restricted to smaller areas than has hitherto been 

 believed. 



Just as all investigation progresses from indefinite to ever more sharply defined 

 knowledge, the results published here indicate a considerable advance on earlier, vaguer 

 descriptions. We seem therefore again justified in giving this summary of our present 

 views and knowledge of the conditions, even if we also hope that future investigations 

 will bring greater clearness and certainty on various points. 



I. The Spaw^ning Regions 



The first investigations on the distribution of the plankton eggs came to the result, 

 well-known from the practical fisheries, that the different species have their own, special 

 spawning places. These must consequently be described separately for each separate 

 species; yet taking all the observations into consideration, certain common characteristics 

 can be detected for some groups of species. In the following we shall therefore give a 

 brief account of the spawning regions of the various species, and then compare these with 

 one another. 



The spawning places on the accompanying charts are based; firstly on the occur- 

 rence of the spawning fish themselves, secondly and mostly on the discoveries of the 

 eggs, thirdly in many cases where no eggs were directly observed on the occurrence of 

 the young larvœ. The last is especially the case for the region west of Great Britain. 

 From this it follows that the spawning places cannot always be given with absolute 

 certainty. 



We have endeavoured to show on the charts by means of different degrees of 

 shading the oceanic regions where the species spawn most and where they spawn least. 

 It can be understood that this mode of representation makes no claim to being quantitative. 

 Although it seems possible from the extensive German, Dutch and Norwegian investiga- 

 tions by means of vertical nets to obtain some notion of the quantitative distribution of 

 the pelagic eggs of our principal species in certain parts of the North Sea, yet a quanti- 

 tative representation of the spawning conditions of the fishes must be reserved for 

 later, more extensive and more detailed investigations. We believe, however, that the 

 method shown corresponds to our present knowledge, as it is also the only one which 

 could be used on the small charts'. 



We possess information regarding 17 species^ of the gadoids. These are in system- 

 atic order: 



1 The heavier lines as also the dark places on the charts indicate much spawning, the fine lines that but 

 little spawning takes place. 



2 Although our knowledge of the developmental stages of the gadoids has made great advances in recent 

 years, it is still impossible to determine with certainty the eggs of various species in the early stages. To 



