THE ORIGIN OF THE MARINE FAUNA. 175 



and we must turn again to the sea to inquire 

 where the primordial animals and plants lived in 

 the days of a lifeless land. 



We have seen that in the sea there are three 

 possible habitats for animals and two for plants. 

 The surface waters of the great oceans bear a 

 characteristic population of animals and plants, 

 the bottom of the sea supports a considerable 

 number of animals but no plants, and lastly 

 the shallow waters exhibit an immense variety 

 of Sea-weeds, Fish, Worms, and other creatures. 

 Which of these three was the original cradle of 

 the great classes of animals and plants 1 



The early discovery of certain animals in very 

 deep water which are closely allied to, if not 

 identical with, some fossils of early geological 

 strata, suggested the idea that a very primordial 

 set of creatures might be found at the bottom of 

 the sea when it was more thoroughly investi- 

 gated ; but as I have pointed out in a previous 

 chapter the hopes of those who anticipated the 

 discovery of a rich Fauna of " living fossils " were 

 doomed to disappointment. 



It is not probable, however, that the abyss of 

 the oceans could have been the cradle of life, 

 even if it had shown a more ancient Fauna than 

 it actually does. 



We cannot tell in what form life first appeared 

 upon the earth. Whether the unstable living 

 substance called Protoplasm was in the earliest 

 conditions of the globe formed spontaneously 

 by the chance combination of its elements, or 

 whether some germ or other made a hazardous 

 journey through space from another planet en- 



