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Part III. — Seventeenth Annual Report 



with the question of migration ; for the present, what we know of these 

 surroundings may be touched upon. 



This subject has been dealt with by the Scotch naturalists Matthews, 

 Ewart, and Brook,* but they did not follow up the relation of the physical 

 and biological surroundings, on the one hand to the wanderings, on the 

 other hand to the bodily structure. 



The first relation has been displayed quite recently by the Swedish 

 scientists, f The herring which occur in winter off the Bohuslan coast, 

 in the Kattegat, appear and swim in the " bank- waters " which are 

 formed by the mingling of the Baltic stream and the Atlantic Ocean. 

 These "bank-waters" have certain distinct qualities, of temperature, 

 salinity, and with regard to the organisms living in them. The correlation 

 thus established is of great importance, and may possibly be regarded as 

 the beginning of greater discoveries. In 1896, the herring fishing off 

 Bohuslan was a failure, and it was found that this was associated with the 

 presence of an abnormal amount of Baltic water. 



So in other places, as with the fluctuations in the quantities of herring 

 off the Scottish east coast, the changes in the spawning places in the Firth 

 of Clyde and Loch Fyne, the reasons will be similar though much more 

 complex. The return of the shoals periodically, year after year, to the 

 same place will depend for the most part upon whether the conditions 

 at those places remain the same. 



On the other hand, Dr. Heincke by his work has been enabled to point 

 out certain relations between bodily structure and the surroundings. 

 How far these are real, of course, only future research can show. 

 Thus, as the salinity of the Baltic diminishes from west to east, the 

 " constitutional size of the ripe " herring becomes smaller — so does the 

 number of the vertebrae and the breadth of the skull ; the body becomes 

 shorter ; the lengths of head and tail become greater, and so does the 

 difference in position between the dorsal and anal fins. 



Again, those herring which grow in very warm, shallow, and brackish 

 water, as those of Schley and Zuyder See, have an extremely small number 

 of vertebrae to the first haemal arch. And again, the herring with the 

 most considerable constitutional size, and likewise the largest number of 

 vertebrae, live on the coasts of the northern North Sea, of Norway and Iceland. 

 These are perhaps most directly under the influence of the salt oceanic 

 waters. Such observations naturally offer a great field of speculation to 

 the physiologist, and — shall we say — also to the "natural selectionist," but 

 for the present we may content ourselves with regarding them as isolated 

 facts until cumulative evidence points to some probable solution. 



The consideration of the relations between the herring and its physical 

 and biological surroundings naturally leads to the question of migration, 

 and here we find Dr. Heincke still more reserved in his conclusions. It 

 has been the custom to think vaguely and talk vaguely of the periodic 

 incomings and outgoings of the herring shoals between the Atlantic Ocean 

 and the North Sea. 



Now, we have no proof of this extensive migration — indeed no signs 

 of it that cannot be explained otherwise, and it may be seen that the 

 whole weight of Heincke's observations is in the scale against it. The 

 division into races simply means division of dwelling-places, and just as 

 there is room enough in the North Sea and Baltic Sea for the gadoids, 

 the pleuronectids, and innumerable other species, there is room enough for 

 a few races of herring. Just as Sir John Murray considered that the 



* Reports of Scottish Fishery Board, I. to V., also by F. G. Pearcey in 1885, but 

 unfortunately, the work of the latter has not yet been read by me. 



f See Summaries by J. T. Cunningham, Journal Marine Biological Association, Vol. 

 IV., 1895-97, p. 233 etseq. ; and by W. Garstang, do., Vol. V., 1897, p. 56 et seq. 



