130 AMEBOID MOVEMENT 



able to state definitely whether it moves in a wavy path. (I have 

 seen this organism only a few times, and on none of these occa- 

 sions was I able to make the test). It seems therefore possible 

 that the agency responsible for the movement of ambas in flat- 

 jed spiral paths can be located at any particular point within 

 the ameba. It seems more likely that this mechanism is a spatial 

 aspect of the intimate colloidal activity occurring in such changes 

 of phase as are associated, with the phenomenon of contractility 

 and streaming. 



Seeing then that movement in spiral paths is possible in animals 

 not possessed of fixed morphology, it becomes of great interest to 

 see whether the spiral paths of free swimming ciliates, flagellates, 

 etc., are similar to those observed in amebas. 



Although the spiral paths of flagellates and swarm spores were 

 first studied by Naegli in 1860, and subsequently discussed by 

 numerous botanists and zoologists, it was not until Jennings in a 

 number of papers ('98-'c>4) on the spiral paths of numerous 

 species of one-celled organisms and rotifers, described the essen- 

 tial facts underlying spiral movement, that the significance of this 

 method of locomotion began to be realized. His work marked the 

 beginning of a healthy reaction against the conception of ridicu- 

 lous simplicity of structure and function which had for several 

 decades been settling upon these organisms. He showed that the 

 spiral path is not a purposeless, senseless reaction on the part 

 of these small organisms, but that it is fraught with meaning, 

 and that it may be regarded as one of the most important of their 

 many activities. 



In a paper "On the significance of the spiral swimming of or- 

 ganisms" Jennings ('01) develops the thesis that spiral swimming 

 is an acquired habit, an adaptation which has become fixed in 

 these organisms so that they would not be condemned to swim 

 in circles, which would necessarily follow from their asym- 

 metrical form. The organism, in other words, swims in a spiral 

 in order to be able to swim in a generally straight course. This 

 explanation involves of course the supposition that the unsym- 

 metrical shape of the body was developed first, and then, since 

 this led to circular paths, revolution on- the long axis became 

 necessary in order that a straight course might be maintained. 



