136 AMEBOID MOVEMENT 



paramecium some of these changes are probably due to shock 

 of some sort, judging from mere appearance; but in many cases 

 the change of direction is preceded by a slowing up of forward 

 movement and the swinging of the anterior end in a wide circle 

 one or more times around. Occasionally one observes slow for- 

 ward movement with wide swinging of the anterior end, for 

 considerable distances. In euglena this condition is more marked 

 than in paramecium; frequently the anterior end spins around 

 with the posterior end as a pivot for several minutes at a time, 

 in low temperatures. 



These observations are strikingly analogous to the circles 

 formed in the paths of amebas in low temperatures, and geomet- 

 rically they bear the same relation to the spiral paths of ciliates 

 and flagellates as the circles do to the wavy path of the ameba. 



Besides the effect of temperature on paramecium and euglena, 

 effects which are continuous and automatic, it is of course well 

 known that the spiral path may be readily broken into by appro- 

 priate stimulation of the sense organs. The automatic locomotory 

 mechanism is then for the time being controlled with reference to 

 the character of the stimulus and the experience of the organ- 

 ism. But as soon as the effect of the stimulus has disappeared, 

 the automatic mechanism again controls locomotion. 



Sense organs of orientation, including organs of equilibration, 

 break in upon the spiral mechanism controlling direction of move- 

 ment, and eliminate its effect. It thus happens that no animals 

 with image-forming eyes or equilibrating organs move in spirals 

 in three-dimensional space when these organs are functional. 

 Conversely, animals without image-forming eyes or equilibrating 

 organs move in spiral paths. In addition to the ciliates, flagel- 

 lates, protophyta, swarm spores and zoospores of algae and fungi, 

 Oscillatoriaceae and rotifers, may also be mentioned the larvae 

 of many worms, echinoderms and molluscs. All these are within 

 the grip of the spiral urge. The grip is indeed slight, as we have 

 seen, but in the absence of stimulation it is none the less absolute. 



The movements of none of the animals in the higher groups 

 have been studied in any detail. Excepting the movements of 

 some of the ciliates, flagellates, ' amebas, rotifers, a few scat- 

 tered protophyta and swarm spores our knowledge of the move- 



