4 SYMBIOGENESIS 



following mainly the outlines of Prof. Keeble's study will be 

 to elucidate the Bio-Economics of Symbiosis primitive and 

 complex, domestic and biological so far as they can be 

 gleaned or inferred from his results and as they must be 

 supplied from other considerations. 



If we hold with Darwin, that all animals and plants are 

 descended from some one prototype, a belief strongly 

 emphasised by modern embryology, we can see that all 

 particular knowledge concerning primitive plant-animals may 

 well be calculated to throw fresh light on the perennial and 

 transcendently important problem of complex symbiosis con- 

 stituted on a grand scale in nature by the inter-relations 

 between plants and animals. "It is genius " according to 

 Prof. J. Arthur Thomson "to give a thrill of fresh interest " 

 to that topic of inter-relations. Though we shall have to differ 

 from Prof. Keeble's exposition of plant-animalism, as far as 

 economic interpretations are concerned, we shall, at any rate, 

 be assisted by it to catch a glimpse of those primordial rela- 

 tions which, I submit, we must assume to have subsisted in 

 the common ancestor of plants and animals, and which must 

 necessarily have gone far indelibly to impress a symbiotic 

 stamp or momentum upon all subsequent organisation. 



Prof. Keeble takes two simple marine worms, Convoluta 

 roscoffensis and Convoluta paradoxa, lowly, unsegmented 

 organisms with a primitive digestive tract, but yet possessed 

 of a well-defined nervous system and efficient sense-organs, 

 although without any proper circulation or excretory 

 apparatus. Soon after they are hatched these small creatures, 

 which live on the edge of the sea in Brittany (and represent 

 Prof. Keeble's Plant Animals), swallow with their food certain 

 algal cells. For a time they continue to feed and grow, and 

 as they do so the swallowed cells divide and multiply, until 

 eventually the masses of these cells occupy a great part of the 

 animal's body and turn it green. The colouring matter is 

 chlorophyll, a substance which, in the leaves of plants, has the 

 power of converting certain inorganic materials into starch, 



