104 PLANT-ANIMALS [OH. 



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. 



In certain circumstances, chlorophyll disappears 

 from the body and Euglena viridis passes into a colour- 

 less phase. When in this state the animal, if it is to 

 feed at all, must do so by ingesting ready-made food. 

 That is, from being a holophytic organism one with 

 a typically plant-like mode of nutrition it becomes 

 heterotrophic, that is, it feeds on ready-made, organic 

 materials, obtained from its environment. After a 

 time, it may reconstruct its chlorophyll and become 

 free once more to manufacture by photosynthesis its 

 organic food-substances from the raw, inorganic 

 materials of its environment. 



If one species of animal can do this, why should 

 not other, even more highly developed species, 

 possess like powers ? Why should there not appear, 

 here and there, animals which resume the habit 

 possessed by their ancestors, construct chlorophyll and 

 become independent, photosynthesising organisms ? 



