THE BALTIC. 23 



the species are found also in the North Sea, so that none are here indigenous. 

 The only differences hitherto observed between the Baltic and oceanic fauna 

 are mere modifications caused by the local surroundings. Such slight changes 

 cannot justify the creation of Baltic species attempted by the Scandinavian 

 naturalists. The salt-water fish which seems to have the best claim to be 

 regarded as a distinct Baltic species is the Gadiis caUarins, or Balficus, a variety of 

 the cod highly esteemed for its flavour. 



But if the fishes that have migrated from the Kattegat to the Baltic are of 

 few species, they none the less abound in numbers. Thus in the Buy of Kiel 

 as many as 240,000 herrings have been taken in a day, each with at least 10,000 

 of the little Crustacea known as the Ta mora lougiconiis in its stomach. Hence in 

 the fishing season of about three weeks' duration over fifty billions of tamora have 

 been devoured by a single species in a single bay of the Baltic* The Odense 

 Fiord, penetrating from the Kattegat into the northern shores of Fyen (Fiinen), 

 teems with excellent cod to such an extent that, for want of a market, they are 

 sold for manure to the peasantry at two or three shillings the cartload. f The 

 organisms swarming in the smallest Baltic inlet must be reckoned by millions of 

 billions. 



The same contrast observed between the open and inland seas also exists 

 between the western and eastern basins of the inland sea itself. West of Rligen, 

 on the shores of Mecklenburg and Lilbeck, the marine flora and fauna present a 

 great many varieties not found in the Gulf of Stettin.+ The eastern basin as a 

 whole is much less thinly peopled than the western, a difference due to its lower 

 temperature and to the brackish nature of its waters, suitable neither for marine 

 nor for fresh-water animals. The organisms that have succeeded in adapting them- 

 selves to this medium are such as are enabled to endure the extremes of heat 

 and cold, and which Mobius accordingly proposed to call Eurythermno. Thus 

 there are here found only sixty-nine species of invertebrates, or about a third of 

 those that frequent the Danish waters § Wherever the water becomes drink- 

 able the marine fauna disappears. The Gulfs of Bothnia and Finland are 

 inhabited exclusively by fresh-water molluscs, and the twenty species of fishes 

 here found are also similar to those of the Finland and Swedish lakes. Thus the 

 Baltic presents the curious example of a sea with two distinct faunas, one oceanic, 

 the other lacustrine. In fact, the sea itself is of a twofold character, by its great 

 southern and western basins forming a gulf of the ocean, in its northern and 

 eastern extremities consisting of open lakes resembling in their phenomena and 

 products the waters of the surrounding mainland. 



* Mobius, "Expedition of the Pomeranin," 1871. 



t Irminger, " Notice sur les i)êches du Danemark," Hevue maritime et coloniale, September, 1863. 

 X "Expedition of the Powfe^-ffwirt," 1871. 



§ 216 species in the western basin; 241 in the whole Baltic (Mobius, «Expedition of the Fome- 

 rania" 1871). 



