48B Miscellaneous. 



peared in English. I send it to you as being likely to interest 

 naturalists in this country. 



36 Royal Terrace, Edinburgh. I am, yours faithfully, 



April 22, 1864. Robert B. Watson. 



The dredgings were made in a little freshwater loch in the island 

 of Christiansund, in Norway, by G. O. Sars, son of Professor Sars. 

 The loch is fed from a peat-moss. In the deeper parts of the loch 

 were found great numbers of Biaptomus Castor, of a blue colour, 

 along with Daphnella brackyura, Polyphemus Pediculus, and a spe- 

 cies of Bosmina {B. obtusirostris). Near the shore, among grass 

 and Nymphseas, were Sida crystallina and two Lynceides, with 

 numerous examples of Acantholeberis curvirostris. 



He then says that from the deepest part of the loch he got up 

 some of the mud, and adds, " I found this, to my astonishment, full 

 of a small red Copepode, in which I at once recognized the salt-water 

 species Harpacticus chelifer described by Lilljeborg. The presence 

 of this Copepode was so unexpected that, in spite of the freshwater 

 forms which I had found, I was obhged to satisfy myself by tasting 

 the water, to be sure it was not brackish. It was perfectly fresh 

 and pleasant to the taste. 



" We thus have here, though on a different scale, an interesting 

 analogy to what has quite recently been observed in some of the 

 great inland lakes, such as the Venern and Vettern*, in Sweden, — 

 viz. that true inhabitants of the sea can, in certain circumstances, 

 gradually accustom themselves to live in thoroughly fresh water. 

 Here, however, the agency of change has not been great, alterations 

 of physical conditions operating throughout thousands of years. The 

 time in this instance has been much shorter. Apparently some very 

 high flood or a furious storm from the west has driven the sea up 

 on some occasion into the loch, which lies close to the coast. Other 

 salt-water species have probably been carried into the loch at the 

 same time, and perished by degrees as the water lost its saltness, 

 while this little Copepode alone was able to survive after every trace 

 of salt had disappeared. It is also interesting to observe the in- 

 fluence which its residence in a foreign medium has had on its mode 

 of life. While, in ordinary circumstances, it is almost exclusively to 

 be found in the very shallowest pools, I found it here, as I have 

 said, in the deepest part of the water, sunk in the mud ; and the 

 same is the case with many of the salt-water forms found in the in- 

 land lakes of Sweden (such as Idothea entomon, Gammarus loricatus, 

 Pontoporeia ajinis). This fact seems to indicate a certain tendency 

 in these forms, when cut off" from their proper habitat, to keep 

 themselves isolated from the true freshwater Crustaceans." 



Further on, in dredging the Mjosen Lake, one of the very largest 

 in Norway, through which flows an immense river, he says : — 



" But my most interesting discovery here was a Crustacean which 



* See Loven, on certain Crustaceans found in the Lakes Venern and 

 Vettern, * Ofversigt af Vetenskabens Akademiens Forhaudlingar ' for 

 1861. 



