CHAPTER II. 

 THE SIMPLEST FORMS OF LIFE 



To approach the problem with any confidence we must 

 study an organism at the very lowest grade of the animal 

 scale. I have pointed out that we have no direct evidence 

 whatever of the nature of those primitive beings with whose 

 origin we are concerned. As has often been said, the first 

 chapters of the story of life have been torn out. The first 

 fossil impressions of living things are found in the Cambrian 

 rocks, at the base of the stratified series. They seem to be 

 the relics or imprints of comparatively large sea-weed or of 

 hydrozoa and similar animals. The story of life must have 

 proceeded for ages before these relatively advanced organisms 

 were enclosed in the mud and sand at the floor of the 

 Cambrian and Silurian oceans. Animals and plants at that 

 stage of development are far removed from the bottom of 

 the organic scale to-day. They must have been preceded 

 by a long procession of softer forms that dissolved in the 

 primitive ocean after death, or were burned up or ground up 

 in the rocks as they formed. 



We turn, therefore, from the paleontologist to the biologist, 

 from fossil to living types of organisms. Here we at once 

 sink far below the level of the hydrozoa and the large 

 multicellular algae. We find a thousand species of bacteria 



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