SYMBIOSIS 49 



it for the manufacture of carbohydrate food. Thus, species of Euglena 

 (e.g., E. viridis), which stand near the parting of the ways which lead, 

 the one to the animal kingdom, the other to the vegetable kingdom, 

 contain chlorophyll, and use it for photosynthetic purposes. Now 

 Euglena viridis is undoubtedly an animal. The single cell or protoplasm 

 of which it consists is provided with a gullet, into which solid particles 

 may pass and thus be ingested by the animal. The membrane which 

 encloses the organism is not composed of cellulose (the cell- wall substance 

 of typically vegetable organisms) and in yet other ways Euglena gives 

 evidence of its ' ' animal ' ' nature. 



Although zoologists and botanists are agreed that the genus Euglena 

 belongs to the animal kingdom, yet it possesses the power of constructing 

 a green pigment chlorophyll which is identical in physical properties 

 with that which occurs in the chloroplasts of plants. Here there is no 

 question, apparently, of any swallowing by Euglena of plant cells. The 

 animal cell makes the pigment in the same way as a plant cell makes 

 it, and, having made it, uses it for photosynthetic purposes. 



Euglena viridis thus seems to present a more reliable and, 

 probably, a more ancestral degree of plant-animalism than 

 Convolute. It is more emphatically than Convoluta indicative 

 of the true ancestral symbiosis from which we may conceive the 

 subsequent bio-economic symbiosis between plant and animal 

 to be descended. Similar to the evolution of sex with its 

 primitive hermaphroditic form, we see how from a compara- 

 tively localised area by means of continuous symbiogenesis 

 with increasing efficiency, a greater differentiation with conse- 

 quent greater progress could be achieved. All that was 

 subsequently necessary to the further step of biological 

 symbiosis was that the partners should have evolved a 

 sufficiency of individuality, of mutuality, and of mutual for- 

 bearance, to remain tolerably complemental though with less 

 confinement, less attachment, and less limitation. 



Again, just as in hermaphroditism perpetual in-breeding 

 is " abhorred " by Nature (see Darwin's classical experiments), 

 so, we may take it, that by the same provident and wise Nature, 

 in consequence of her bio-economic necessities, a state of 

 (predaceous) "in-feeding," such as the summary exploitation 

 of the green cells of Convoluta, is " abhorred." It is relations 

 leading to abiding gains, abiding values, that are required 



