42 Routes from the Sea 



This is interpreted as indicating that the hag-fish had no fresh 

 water ancestors" (Bond, Gary, Qc Hutchinson, 1932) . 



The waters in the great seas of the earth constitute a great physi- 

 cal-chemical system which maintains more or less stabiUty. Changes 

 in the open sea, except for temporary surface dilutions resulting 

 from rains, are chiefly due to the activities of organisms (Mc- 

 Clendon, 1918) . In warm seas water is supersaturated with calcium 

 carbonate, and lime is continually precipitated out, largely through 

 the activities of organisms. Bottom deposits in parts of the ocean 

 within the 2000 meter contour may contain 1/2 to 2/3 lime (John- 

 stone, 1908) . Ocean water contains a great variety of substances in 

 solution in forms available for use by plants and animals. Marine 

 animals make use of such metals as copper, zinc, iron, and manga- 

 nese (Phillips, 1922) . With the inflowing waters from land areas 

 also come various substances. Among these, compounds which con- 

 tain nitrogen in available forms are of primary importance. They 

 result to a considerable extent from the work of nitrogenous bac- 

 teria, which are largely confined to the land. Because fresh water 

 has average depths that are much less than those in oceans, light 

 should be available more generally for photosynthesis and the initia- 

 tion of the manufacture of basic foods. But fresh water, because it 

 is shallow, is usually more turbid than sea water, and thus the pene- 

 tration of light is prevented. It also remains more turbid because 

 precipitation is more rapid in salt water. When the fundamental 

 needs of the basic activities of protoplasm are considered, there are 

 desiderata in both fresh water and sea water. In the past and at 

 present animals are struggling to pass from one to the other. Usu- 

 ally the chief limiting factor in the productiveness of any area is 

 available food. Nitrogen and phosphorous compounds are perhaps 

 those which most often are present in minimum amounts and thus 

 limit the manufacture of organic foods, growth, and reproduction. 



There are many examples of animals that have been cut off from 



