32 PRIMITIVE ANIMALS 



manner of animals and now in the manner of 

 plants, they seem to constitute a connecting link 

 between animals and plants and to stand at any 

 rate near to the branching of the road which led to 

 the great dichotomy of all living things. That the 

 Flagellata are truly in this position is supported 

 by the widespread occurrence of a flagellated phase in 

 the life-history of so many unicellular animals and 

 plants, as well as in the spermatozoa of practically 

 all the Metazoa and of the more primitive Metaphyta. 

 We set out from the standpoint that any theory 

 of the origin of life should take account of the funda- 

 mental facts of assimilation, as lying at the very 

 basis of all vital processes. If we assume that life 

 at its origin had any of the properties of the simplest 

 forms of life as they now exist, we can hardly escape 

 from the conclusion that the presence of chlorophyll 

 was the necessary precursor of life. We must of 

 course admit that chlorophyll in the present state of 

 nature is only produced by life, so that the origin of 

 the chlorophyll itself is a problem as cogent and as 

 obscure as that of life. If however we prefer to do 

 without chlorophyll, and conceive of the first living 

 things as existing without this substance, then we are 

 supposing the existence of a state of life about which 

 we can predicate nothing, the continuance of which 

 must have depended on entirely unknown properties, 

 for the ascertainment of which we have at present no 



