THE OCEAN 185 



environment are important. It is certainly 

 impossible to imagine a medium more rich and 

 varied in elementary constituents than sea 

 water, unless it be sea water with still other sub- 

 stances added to it. But, in the first place, 

 there are few absent elements which might 

 be added, and, in the second place, the addition 

 of other substances would be likely to cause 

 the escape of bodies which are present. At 

 all events, the ocean is certainly more favor- 

 able in these three respects than if it were 

 anything else that could occur in the course 

 of nature. Almost ideally mobile, rich, and 

 varied, the sea is an almost perfect source of 

 supply for a complex mechanism. To be 

 sure there are great difficulties in extracting 

 its constituents from sea water, and the 

 efficiency of physiological processes is a factor 

 essential to their utilization, but at least 

 there stand materials ready for the mechanism 

 which can employ them. 



The predominance of water, no doubt, forces 

 that substance upon living beings as their 

 chief constituent; in view of the fitness of 

 water for the purpose that is in itself a favor- 

 able circumstance. Otherwise the organism 

 is left free to choose from all the common 

 elements, and from some of the rare ones, what 

 may be most suitable to its purposes at every 



