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president’s address. 
Of the first kind I can only mention Mysis relicia, which 
was found at the bottom of the Scandinavian Lakes by Loven, 
and more recently in the North American Lakes, in Ireland, 
and in Germany, and is almost identical with Mysis oculata, 
inhabiting the North Sea ; and the fresh water Medusa 
Limnocnida, found in Lake Tanganyika by Moore. 
The presence of such aberrant fresh water types has given 
rise to the hypothesis that the lakes, which they now inhabit, 
were formed by being cut off from the sea, and such lakes 
have, therefore, been called “ Reliktenseen.” 
But to stamp every lake in which a “ Reliktenfauna ” has 
been found, without reference to the geological features, 
as a former arm of the sea, is, as Forel points out, without 
warrant, and we must look to some other agents of dispersal 
(£.g., perhaps even birds) to account for the facts. 
An interesting paper has recently appeared by Samter on 
the distribution of Mysis r elida and other “ relict ” forms 
in Germany, from which it appears, that of more than 
forty lakes investigated, in no case was this species found 
in a single lake which drained into the North Sea, but only 
in those whose effluents run into the Baltic. 
From this the author draws the conclusion that Mysis 
r elicta originated from the Mysis oculata form at a period 
when the Baltic was an inland lake (known to geologists as 
the Ancylus sea) at the end of the Post-Glacial period, and 
then reached their present habitat by migration up the 
rivers. These forms are in fact “ relictenfauna ” of the 
northern glacial sea, and do not show in any way that each 
lake in which they occur is a “ relictensee.” 
That limnetic forms have occasionally, at any rate, arisen 
by immigration from the sea and a gradual adaptation to 
the new conditions is shown by the case of Cordylophora, 
which so recently as the middle of the last century was only 
known to occur in the brackish water of estuaries. Since 
