THE MOVEMENTS AND REACTIONS OF AMCEBA. 141 



(Fig. 38, anterior end). Further, such particles, after making one or 

 two revolutions, usually become detached and drop oft'. 



It is thus clear that Amoeba -verrucosa and its relatives have what 

 may be called a rolling motion ; a given spot on the outer pellicula 

 passes forward on the upper surface, downward at the anterior end, 

 remains quiet on the lower surface, passes upward at the posterior 

 end, and again forward. Its movement may be compared directly with 

 the movement of a given point on the circumference of a wheel that is 

 rolling forward. A diagram of the movement of a particle on the 

 surface as it would appear in a side view is given in Fig. 40. 



Certain details of the movements are interesting, and may best be 

 brought out by description of specific observations. In one case two 

 small particles had become attached, a short distance apart, to the surface 

 of a specimen of Amoeba sphczronucleolus. They were at first side by 

 side and a little to the right of the middle line, one somewhat farther 

 to the right than the other (Fig. 41). They moved forward in parallel 

 courses, and reached the anterior edge at the 

 same time, passing over the edge and to the 

 under surface. It now required two and one- 

 half minutes for the Amoeba to pass over p 

 them, during which time they remained nearly 

 or quite at rest. They then moved upward 

 to the upper surface and forward again. The 

 one nearer the middle line moved a little 

 faster than the other, reaching the anterior edge in two and three- 

 quarter minutes, while the lateral one required three minutes. Both 

 emerged at the posterior end again at the same time, the central 

 one having remained quiet three and one-fourth minutes, while the 

 lateral one had been three minutes at rest. The next forward course 

 required, respectively, but one and one-half and two minutes, the central 

 particle moving the more rapidly. The two particles were no longer 

 side by side, the central one being now a little in advance. The latter 

 spent after the next turn two and one-half minutes on the under surface, 

 while the lateral particle spent but two minutes, so that they came up 

 from the posterior end again at the same time. 



The two particles started forward again and had reached the middle 

 of the upper surface when the Amoeba ceased its forward movement, 

 loosened its anterior end from the bottom, and became attached by its 

 posterior end. After five minutes it began to move again, but now in 



* FIG. 41. Paths of two particles attached to the outer surface of Antoeba 

 sphceronucleolus as described in the text. That portion of the paths which is on 

 the lower surface is represented by broken lines. (No attempt is made to rep- 

 resent the forward movement of the Amoeba in this figure.) 



