in time, we can see how the primordial waters 

 would become rarer and rarer in those earth- 

 derived elements that compose the content of the 

 present existing sea. Conversely, so to say, the 

 ocean became saltier with each succeeding age 

 . . . What plainer proof could my experiment 

 give to establish the fresh-water ancestry of the 

 serpent-star? Is it not more than extremely prob- 

 able that the echinoderms having had their be- 

 ginning in a deep and relatively saltless sea, and 

 bearing the impress of the passing ages in their 

 increasingly saline environment have so com- 

 pletely conformed to their marine habitat, in struc- 

 ture and the chemistry of their growth, that it has 

 marked them forever as its very own? 



If further proof were necessary to establish that 

 it is because of chemical properties in the water 

 that the echinoderms have become identified only 

 with the sea, I should need merely to add that a 

 slight excess of the necessary material is as pro- 

 found in its influence as is a deficiency. Similar 

 structural results to the experiment that I have 

 just reviewed, can be achieved by adding a trace 

 of potassium chloride to sea-water containing the 

 normal amount of lime. 



[105] 



