AMEBOID MOVEMENT 113 



the approach of the division crisis did not tend to destroy the 

 action of the wave mechanism, but only slowed down movement 

 and shortened the waves. The path of one of the daughter 

 amebas was followed for a short time, in which there is evidence 

 of a wavy path, but it soon came upon a small mass of debris 

 which it ingested and soon thereafter reversed its direction of 

 movement. This behavior made it unprofitable to continue further 

 observation of this ameba. For the gradual change in direction 

 to the left from wave I to 6 in the path of the parent ameba, no 

 adequate explanation has suggested itself. 



That amebas react to light has been shown by Verworn ('89), 

 Davenport ('97), Harrington and Learning ('oo), Mast ('10) 

 and especially Schaeffer ('17). It appeared desirable therefore 

 to control the rays of light, for it was thought possible that light 

 might be a factor in the formation of the wavy path. Since no 

 method has yet been devised that permits of the observation of 

 the path of the ameba other than a succession of camera lucida 

 outlines, it is impossible to omit light altogether in the experi- 

 ments. The next best procedure was therefore followed, viz., 

 the alternation of periods of darkness of a few minutes' duration 

 with brief ten-second periods of light, to permit the drawing 

 of camera lucida outlines. The dish in which the amebas were 

 observed was placed in a light-tight box and all light excluded 

 except that which passed through "Daylite" glass with an opal 

 surface on both sides between the condenser and the light source. 

 None but parallel beams, passed through a condenser, reached 

 the ameba. The metal parts of the objective were also blackened. 

 The work was done in a dark room. 



Figures 34 and 35 show sections of the path of two Amoeba dis- 

 coides under these experimental conditions. The amebas were 

 for the most part in clavate shape, which is the most favorable 

 shape for the formation of smooth waves. In figure 34, from 

 2:29^4 to 2:42*4 the ameba was in continuous light. A section 

 of a little more than one wave is shown. Although pseudopods 

 were thrown out at considerable distances to the right and left 

 of the path, a smooth, wavy path was nevertheless maintained. 

 At 2 :42*/ the light was turned off until 2 :58^ except for two 

 ten-second flashes at 2:47 an d 2:52. During the first period of 



