154 NEW YORK STATE MUSEUM 



Among 610 individuals of various marine species which were grad- 

 ually accustomed to fresh water, only 37 per cent died. Of the 

 same number of the same species which were kept at the same time 

 continuously in salt water, 34 per cent died; so that the mortality 

 in the groups compelled to live in a strange element was only 3 

 per cent greater. These experiments show that sea animals are 

 not bound to an absolute quantity of salt, but their stenohaline 

 or euryhaline behavior is important in this, that they are able more 

 easily or with more difficulty to adjust the salt content of their 

 tissue to that of the surrounding water. It has been found that 

 nearly related species behave very differently in this respect; one 

 species may die immediately, another live on for several days. Fora- 

 minifera live mostly in pure salt water, yet in the estuaries of British 

 rivers there are known 100 species belonging to 44 genera. In 

 brackish sea water, in spite of the simultaneous increase in the lime 

 content, the secretion of lime skeletons is diminished. Species of 

 Foraminifera in the estuaries have shells poor in lime, while the 

 same species secrete coverings rich in lime in the normal salty sea 

 (Walther, 1894, p. 63; 1919, p. 123). 



A noted area for studying the influence of a diminished salt 

 content upon the animal life is the Baltic sea, which shows a very 

 striking decrease in salinity eastward and in a large way the responses 

 of the fauna to it. It is more static than estuaries ; it lacks the tides 

 which are characteristic of the latter and therefore does not show 

 the pronounced changes from fresh to salt water twice a day. The 

 North sea has the normal marine salinity of 35 permille which 

 decreases steadily going eastward in the Baltic until at the northern 

 end of the Gulf of Bothnia the water is practically fresh. In the 

 Skager Rak the water has a salinity of 34 permille; -off Skagen, 

 the northeasternmost point of Denmark, 30 permille; in Kattegat, 

 22 permille, and 20 permille in Kiel bay. " Throughout the southern 

 part of the Baltic, from the ' Scheren,' at the mouth of the Gulf 

 of Finland, to Bornholm the salinity is from 7 to 8 permille at the 

 surface and does not vary greatly in the depths. For instance, 

 in the deepest part of the Baltic off the Island of Gotland, the salinity 

 is only 12 permille, and in the Bay of Danzig, which shows a yearly 

 average of 7.22 permille at the surface, it is only 11.66 permille 

 (average) at the depth of 105 meters. In the Bay of Riga the 

 salinity is 6 permille, in the southern part of the Gulf of Bothnia 

 it is 4 permille and gradually diminishes until the water is entirely 

 fresh (3 permille at Uleaborg, northern end; Grabau, p. 1045). 



