THE ORIGIN OF LIFE 31 



A good example of these Flagellata, which can with 

 difficulty be classified either as an animal or a plant, is 

 Euglena viridis (Fig. 5 B), a very common organism, 

 which is often responsible for the bright green scum 

 that collects on the surface of puddles and ponds. 

 Such a green scum is often found to consist of a 

 mass of small green organisms which wriggle and 

 swim in the water by means of a flagellum and by 

 the contractions of the elastic body-wall. Euglena 

 viridis contains chlorophyll by means of which it 

 can assimilate carbon dioxide (C0 2 ), and accumu- 

 lations of starch-like substances are found in the 

 body. It can flourish on purely inorganic substances 

 like a green plant, but its animal properties are 

 shown in its possession of a mouth, its capacity for 

 assimilating organic food, and in the fact that it 

 possesses a pigment spot sensitive to light. Though 

 we may admit that the plant nature of Euglena 

 preponderates over the animal nature, yet there 

 are close relations of Euglena among the Flagel- 

 lata which are complete animals in their manner 

 of nutrition, and which no one would hesitate to 

 classify as animals. The Flagellata as a group can, 

 therefore, be confidently ascribed neither to the 

 animal nor to the plant kingdom. In their mo- 

 bility, the absence of a cellulose cell-wall which is 

 present in all undoubted plants, and in the peculiar 

 elasticity with which they assimilate now in the 



