104 life's beginning on the earth 



are indispensable for any form of life. All living things are 

 bathed in a watery fluid. They either live in it or contain 

 within themselves a water solution with some salt in it to 

 bathe all their vital organs. Viewed from this angle the 

 great puzzle of life takes on a novel aspect. 



Further evidence to substantiate the view that oceans are 

 the cradle of life is found in the fact that they display a 

 greater diversity of plant and animal life than do lakes, 

 rivers, or the dry land. We find in the sea, particularly, 

 certain primitive animals which have hardly any blood or 

 tissue-juices, but are perfused everywhere by the sea-water. 

 An example is the common jelly fish, which resembles loose 

 pieces of transparent flesh. Such animals depend entirely 

 upon the sea-water for their existence. They cannot live 

 in rivers or lakes or after the waves have thrown them on 

 the beach. 



But more independent types of life evolved during mil- 

 lions of years, while many forms appeared, and again dis- 

 appeared, unable to maintain and propagate themselves. 

 Little by little the outer skin enveloping the organism be- 

 came denser. A better protection was afforded, but the 

 tissues inside were thus shut off from the sea water, which 

 had removed waste products and also brought dissolved 

 air to every cell of the animal's body. 



So thick-skinned organisms survived only if they devel- 

 oped organs which provided for an intake of air (gills or 

 lungs); organs which provided for carrying around the dis- 

 solved air to all cells (a beating heart and blood vessels) ; and 

 finally, organs for removing waste from the liquid circulat- 

 ing inside the organism (kidneys or organs like them). 



Just how all these complicated organs developed is quite 

 incomprehensible at the present stage of our knowledge, 

 but we ought to remember that (he ways and means avail- 

 able for development are infinitely more plentiful than we 

 can imagine. 



