D.—ZOOLOGY. 77 
and coastal herrings that spawned in winter or spring near the coasts, 
often in brackish bays or in estuaries. The herrings of the Baltic are 
coastal herrings, but those of Iceland and of Norway form a third class— 
herrings of the open sea that spawn in the spring. It seems to me highly 
probable that in the North Sea the coastal communities have been derived 
from those of the open sea, that they have changed their habits but kept 
to their original spawning season, whereas the others may have postponed 
their spawning, waiting for the influx of the oceanic water. 
Diincker has shown that the plaice of the Baltic differs from that 
of the North Sea in having an average of one vertebra less, five rays less 
in both dorsal and anal fins, and one ray more in the pectoral fins. The 
Kattegat plaice agrees with that of the North Sea in the number of 
vertebre and of dorsal and anal rays, afd with the Baltic plaice in the 
number of pectoral rays ; but it differs from both in its deeper form. There 
is no doubt that the plaice of the Baltic, the Kattegat and the North 
Sea form separate communities ; there is nothing to prevent a Kattegat 
plaice from going either into the Baltic or into the North Sea if it wants 
to; but it seems not to want to—it has its own feeding places and breed- 
ing places and prefers to keep to them. 
I have studied with particular attention the fishes known as char, 
or salmonoid fishes of the genus Salvelinus. Char are very like trout 
in appearance, but have orange or scarlet spots instead of black ones; 
they inhabit the Arctic Ocean and in the autumn run up the rivers to 
breed in fresh water, often forming permanent freshwater colonies in 
akes. There are many such colonies in the lakes of Scandinavia, of 
Switzerland, and of Scotland, Ireland, and the Lake District of England ; 
he formation of these colonies must date back to glacial times, when these 
Arctic fishes occurred on our coasts and entered our rivers to breed. 
These lacustrine communities show considerable diversity in habits, and 
so in structure ; for example, the char of Lough Melvin in Ireland are 
quite unlike those of Loch Killin in Inverness in form, in coloration, in 
the shape of the mouth, and in the size of the scales ; these differences are 
sufficient to entitle them to be regarded as different species, and I have 
so regarded them ; but now I doubt whether it is not better to look upon 
all these lacustrine char, however well characterised, as belonging to the 
same species as the migratory char of the Arctic Ocean, for once you begin 
giving specific names to lacustrine forms of char you never know where to 
stop. But if we were to exterminate the char in our islands and on the 
Jontinent, except in a dozen selected lakes, we should have left a dozen 
ve Lmarked forms which it would be convenient to recognise as species. 
somewhat similar problem arises in the classification of man ; it is con- 
venient to place all the living races in one species. But if there were only 
Englishmen and Hottentots we should probably regard them as specifically 
ustinct. 
_ In our British char, habitudinal segregation—the formation of com- 
munities in lakes—has been followed by a geographical isolation which 
commenced at the end of the glacial period, when the migratory char 
retreated northwards. The char of each lake have evolved separately, 
d one can see clearly how many of the differences between them are 
ated to the conditions of life; for example, the large eyes of the Loch 
annoch char, which lives in a very deep lake, and the blunt snout and 
