THE MOVEMENTS AND REACTIONS OF AMCEBA. 145 



lower surface of the cover glass I was able to define with some accuracy 

 the parts that were attached and those that were not. A small flagel- 

 late was moving briskly about between the Amoeba and the cover glass, 

 but its excursions were limited by a visible line running parallel with 

 the anterior edge of the Amoeba and extending at the sides back to 

 about one-third the animal's length from the rear (Fig. 43, a-a-a). 

 The zone between this and the margin was pressed close to the glass, 

 and was evidently attached to it The more pointed posterior end was 

 held quite away from the glass, leaving a broad passageway through 

 which the flagellate finally escaped. 



The results of this observation were confirmed by another. An 

 Amoeba verrucosa in full career was suddenly turned on one lateral 

 edge by a strong current from a rotifer, and its upper edge coming in 

 contact with the cover glass, it remained in that position some time 

 without change of form. It could be seen that the under surface was 

 concave, the edges very thin and flat, while the 

 posterior portion was thick and arched (Fig. 44). 



It is clearly at the advancing edge of the ani- 

 mal that the most active movements are taking 



O 



place. Here the hyaloplasm may be seen to 

 push forward in a series of short waves, the 

 anterior edge of each becoming attached to the 

 substratum. At the same time, of course, an 

 equivalent amount of protoplasm becomes de- ''%&/ 



tached from the substratum along the line a-a-a, 



FIG. 43.* 

 Fig. 43, though this does not take place in 



waves, so far as observable. The anterior wave must in some way 

 pull upon the upper surface of the Amoeba, bringing it forward, and 

 dragging with it the elevated sac-like posterior end. A certain feature 

 of the advance of the anterior edge seems of much significance. Each 

 wave seems to arise just behind the previous anterior boundary line 

 and overlaps it, leaving it buried. This line often remains visible for 

 a short time after the new wave has been formed. The new wave 

 rolls over the preceding one in such a way that its original upper 

 surface becomes applied to the substratum. This is demonstrated by 

 the rolling under of small objects on the upper surface of the advanc- 

 ing wave. A diagram of the movement at the anterior edge is given 

 in Fig. 45. The movement can be imitated roughly by making a 

 cylinder of cloth, laying it flat on a plane surface, and pulling forward 



* FIG. 43. Attached surface of Amoeba verrucosa, creeping on the lower surface 

 of the cover glass. The unshaded portion in front of the line a-a-a is attached 

 to the substratum, while the shaded portion is free and raised slightly above 

 the substratum. 



