8o 



AMEBOID MOVEMENT 



Figure 29. a, a particle attached to an ameba and moving at the same 

 rate as the ameba. This condition is often observed in proteus where the 

 surface film, owing to its destruction during the formation of the longi- 

 tudinal ridges, retards the forward movement of this layer, b, a particle 

 attached to the surface film of an ameba moving twice as fast as the 

 ameba. This condition is seen in discoides, vcrrucosa, sphaeronucleosus, 

 etc. c, a particle on an ameba that does not move at all although the 

 ameba does. This is seen when a heavy particle is laid on an ameba, too 

 heavy for the surface film to move, d, movement of ectoplasm in an ameba 

 suspended in a jelly medium. The vertical lines are to be considered as 

 stationary. 



the rate of movement of the various tissues of the ameba from a 

 single standpoint, a point outside of the ameba, little room is 

 left for confusion. 



There is comparatively little friction, if any at all, between the 

 upper surface and the endosarc, according to Jennings' view, since 

 both these layers move at the same rate and as a single stream. 

 On the other hand there must be very considerable friction be- 

 tween the endoplasm and the lower ectoplasm, which does not 

 move at all. This difference in the amount of friction must show 

 itself in the different speeds of the endoplasm near the upper 

 ectoplasm and near the lower ectoplasm. Observation indicates 

 however that the most rapid streaming of the endoplasm is in 

 the middle of the ameba or pseudopod and that it gradually be- 

 comes slower as the ectoplasm is approached on all sides. 



We said above that if the ectoplasm were a more or less 

 permanent skin in which the ameba rolled as described by Jen- 

 nings, the upper surface ( =ectosarc, Jennings), according to a 

 well known mechanical principle, would have to move ahead 

 about twice as fast as the ameba advances. Now the upper sur- 



