CHAPTER XIII 



THE WAVY PATH OF THE AMEBA AND THE SPIRAL PATHS 

 OF ClLIATES AND OTHER ORGANISMS 



The most interesting feature of the path of the ameba is of 

 course the waves. The path of an ameba closely resembles the 

 projection of a helical spiral on a plane surface, and this at once 

 calls to mind the spiral swimming of flagellates, ciliates, rotifers, 

 larvae or various groups of animals, swarm spores and zoospores 

 of various algae and fungi. But before we take up the general 

 subject of spiral movement, it will be worth while to see what 

 other evidence there is beside the wavy path, that indicates that 

 the "spiral urge" is present in the ameba. 



It is well known that in a number of the small amebas, especially 

 the soil amebas, there are two trophic stages, an ameboid stage 

 and a free swimming flagellate stage. The change from one 

 stage to the other is a matter of a few minutes only. In the 

 flagellate stage (Figure 43) the amebas resemble a small flagellate 

 like chilomonas, very closely. Their manner of swimming is very 

 similar. And it is especially noteworthy in this respect that they 

 revolve on their long axis and describe a well marked, regular 

 spiral path, just as do the flagellates and ciliates. Unfortunately 

 no records have yet been made of the paths these amebas describe 

 when in the true ameboid stage. Since, therefore, as we shall see 

 later, the slightly unsymmetfical shape of the flagellate stage is 

 not the cause of the spiral path, it is probable that the mechanism 

 controlling the activity of the flagellum can produce orderly loco- 

 motion only when the organism follows a spiral path. 



Much has been written about the fundamental similarity or iden- 

 tity between flagella and pseudopods. All writers who have ex- 

 pressed themselves on this point incline to think that there is such 

 similarity, that flagella are really very slender and very agile 

 pseudopods. I am not going to record here the evidence for this 

 conclusion, for I have recently had the good fortune to make some 

 very convincing observations on a hitherto undescribed ameba 



126 



