CHARACTERISTICS OF ASSOCIATIONS 17 



the origin of protoplasm." Further, according to Osborn, 

 " it appears that every subsequent higher life phase — the 

 bacterial phase, the chlorophyllic algal phase, the proto- 

 zoan phase — were also primarily of fresh-water and second- 

 arily of marine habitat. From terrestrial waters life may have 

 gradually extended into the sea." 



Of considerable interest to us are Osborn's remarks on 

 the great antiquity of most of the marine invertebrate groups 

 and the extraordinary persistence of type, which is such that 

 forms " with an antiquity estimated at 25,000,000 years 

 can be placed side by side with existing sea forms with very 

 obvious similarities of function and structure." Again, 

 a comparison of fossil and modern Polychaets, both swimming 

 and burrowing forms, affords clear evidence that the 

 Cambrian sea-shore and its tidal conditions closely resembled 

 those of the present day. 



Macfarlane (19 18) takes the view that life originated in 

 thermal fresh-water areas, the earliest forms being probably 

 colourless bacterial forms similar to the thermal sulphur 

 bacteria. From these slowly originated the unicellular 

 blue-green algae which, by a process of gradual accommoda- 

 tion to cooUng terrestrial conditions in fresh water, or in 

 moist places and later in the sea, gave rise to a wealth of 

 species that became in turn the ancestors of all green plants. 

 Similarly, by a train of arguments we have not space to 

 follow, a lacustrine origin is claimed for animals. 



Simroth (i 891), in analysing the factors and reviewing the 

 various possibilities necessary for the first production of life, 

 in this connection remarks that this could not have taken 

 place in the hydrosphere without the concurrence of air, since 

 respiration is one of the first and most essential functions 

 of Hfe. On an a priori view, therefore, the most favourable 

 point for the first appearance of life would be where the two 

 essential factors, air and water, interact most effectively. The 

 question of an abyssal origin of life is thus, to all intents and 

 purposes, excluded, and all that remains to be decided is 

 at what part of the ocean's surface the exchange between 

 air and water could take place most favourably, whether in 



c 



