AMEBOID MOVEMENT 23 



its identity as a rule; that is, as the ameba moves forward, the 

 ridge in effect moves back over the ameba to lose itself in the 

 wrinkles at the posterior end (See Figure n, A). The number 

 of ridges on any random selection of amebas is variable, and is 

 moreover difficult to state. A large ameba may have as many as 

 six or seven side by side on its upper surface. The number on 

 the sides and on the lower surface are difficult to estimate. The 

 space between ridges is about equal to the width of the ridges, 

 but as one passes toward the posterior end, the ridges become 

 more closely crowded together. 



From thes"e observations on the formation of ridges it is evi- 

 dent that they do not represent a wrinkling of the surface such 

 as occurs in a semi-rigid curved surface when it is made to 

 occupy a smaller space. The ridges are wrinkles only in ap- 

 pearance, not in origin. The surface of the ridges is younger 

 than the space between them. It appears as if the pseudopod 

 which has to widen as it increases in length, could not liquify the 

 ectoplasm uniformly all around, but only in longitudinal strips 

 here and there, and that through these openings the ectoplasm then 

 flows. There is no question about the greater readiness with 

 which ectoplasm is formed in this ameba as compared with 

 many others, but after a careful comparison of proteus and 

 carolinensis, where ridges are formed, with discoides (Figure 

 n, B), dubia (Figure n, C}, laureata (Figure 4) and annulata, 

 where none are formed, the only conclusion presenting itself is 

 that the visible physical properties of the protoplasm of proteus 

 and carolinensis give no hint as to the cause of the presence of 

 ridges in these species. The protoplasm of discoides and laureata 

 is about as viscous as that of proteus, yet in these there is never 

 any ridge formation. 



The ridges in proteus recall, of course, the ridges always ob- 

 served in verrucosa, sphaeronucleosus (Figure 13) and their con- 

 geners, especially while the latter are in locomotion. A sphaero- 

 nucleosus is especially favorable for study in this connection be- 

 cause, of its greater activity. This ameba has four or more longi- 

 tudinal ridges on its upper surface, while in- locomotion, which 

 strongly resemble those in proteus and carolinensis. The chief 

 difference lies in the fact that in splweronucleosus the ridges are 



