30 PRIMITIVE ANIMALS 



among organic carbon compounds which have been 

 elaborated by the action of other animals or plants. 

 This is the reason why bacteria always congregate 

 in decaying animal and vegetable matter, and it 

 would seem that their existence presupposes the 

 existence of other forms of life to supply them with 

 the requisite combined carbon. 



We are left therefore with the chlorophyll-possess- 

 ing green plant as the conceivable starting point for 

 living matter. From the point of view of the problem 

 of assimilation, the green plant is in much the most 

 independent position, as it can form its own substance 

 from inorganic matter without the aid of other living 

 beings. It is indeed difficult to escape from the 

 conclusion that the earliest living organisms pos- 

 sessed chlorophyll, as, without the power of combining 

 inorganic carbon, the continued growth of living 

 substance seems, as far as our experience goes, to 

 be an impossibility. 



There is a large group of unicellular organisms 

 now in existence, the Flagellata, which propel them- 

 selves through the water by means of one or more 

 whip-like cilia, some of which are without chlorophyll 

 arid must be considered as animals, since they nourish 

 themselves on already elaborated organic matter 

 while others possess chlorophyll and have the power 

 like any green plant, of nourishing themselves on 

 carbon dioxide and purely inorganic compounds. 



