44 



ORGANISMS OF ONE CELL 



ordinary water plants/m the stems of which /t is often abundant. 

 It varies in size from i/2ooth to 1/7 5th of an inch and under- 

 goes different form changes which at times make it difficult to 

 recognize. There is some question whether some of the species 

 described as different species are not in reality, one and the same, 

 the matter can be decided only by knowledge of the complete 

 life history. Sometimes the organism is flattened or spatulate 



V 



IF/ 



FIG. 18. Amoeba proteus in active moving condition, c.v., Contractile vacuole; 

 f.v., food vacuole; n, nucleus; w.v., water vacuoles. The arrows indicate the 

 direction of protoplasmic flow. (From Sedgwick and Wilson.) 



in form changing slowly, if at all, in shape. Again it becomes 

 a quickly moving drop of protoplasm quite transparent and 

 long drawn out as a single thread of substance. All interme- 

 diate grades between these forms are known, and in a general 

 way, the form and movements indicate states of nutrition for 

 the flat spatulate types are usually dense with undigested food 

 while the rapidly moving forms are relatively clear and trans- 

 parent (Fig. 18). 



Nucleus. While the form of the organism is continually 



