48 THE EVOLUTION OF THE META20A 



The first and the most important problem we meet here is 

 which of the two opposite large biotopes of the sea is primary ; 

 benthos (the bottom of the sea), or the pelagic zone (the zone 

 of the free water) ? 



It can soon be found if we make a physicochemical compa- 

 rison of the sea properties, that it was in all probability the 

 sea bottom where the first life came into being. This was the 

 only place where Ufe w^as initially able to develop further. 

 It must have been in the shallow water that sunrays could 

 penetrate down to the sea bottom and where the early Life of 

 animals could develop and be sustained on algae and on bac- 

 teria. Individual types of animals could later get used, by 

 way of special adjustments, to the Hfe on a deeper sea bottom, 

 or they could begin to inhabit as plankton the free water 

 area. It is very probable that the Ufe on the deeper sea bottom 

 of the abyssal zone developed much later than that in the 

 plankton. In the plankton, Ufe reached an exuberant growth 

 and sank as an organic rain to the unproductive sea bottom. 



Purely inductive thinking alone allows us to suppose that in 

 free water the animal Ufe began to develop in a similar way. 

 First it was necessary that phytoplankton appeared which syn- 

 thesized the organic substances and served as a basic food for 

 animal consumers. The substance of a Uving organism has 

 a greater specific gravity than the sea water (in the remote past 

 this difference was probably even greater than it is now); or- 

 ganisms had therefore to depend on the sea bottom until 

 finally individual small algae— it was easier for these to do so — 

 succeeded in developing mechanisms which helped them to 

 overcome the effects of gravity, i,e. to lower their specific gra- 

 vity, as was done, for example, by unduUpodia (flagella, drops 

 of oil, gelatinous coverings Ughter than sea water, excres- 

 cences and similar forms of the body that increased the friction 

 between the body and water). 



It is certainly not a mere chance that we find the phyto- 

 plankton of the sea to be composed exclusively of monoceUu- 

 lar small algae and that no higher type of plants had been able 



