Protozoan Studies 267 



an extension at a distant point. Dellinger ('06) supposed that 

 there are strands of denser protoplasm running through the endo- 

 sarc, and gives as evidence the observation that an elongated 

 ingested diatom v^ill move freely along w^ith granules in the endo- 

 sarc when it lies lengthwise to the direction of flow, but will stop 

 when turned sidewise, as though the meshes between the strands 

 were greater than the breadth but less than the length of the 

 diatom. The same effect might be produced, however, by the 

 resistance of the ectosarc when indented by the diatom. The 

 diatom with its silicious shell would probably be heavier than the 

 endosarc and press against the "ventral" wall of ectosarc. If it 

 were lighter than the endosarc it would press against the "dorsal" 

 body wall of the Amoeba. In either case the resistance against 

 being swept along by the current of endosarc would be less when 

 it lay lengthwise than when it lay crosswise to the direction of 

 flow. 



To demonstrate this I measured the force required to pull an 

 ordinary glass sHde over the surface of a soft gelatine plate under 

 water. It required 2548 dynes when placed crosswise but only 

 2078 dynes when placed lengthwise. The same would hold for 

 the diatom if it were heavier than or lighter than the endosarc. 

 The current of endosarc would act on a larger surface when the 

 diatom were placed crosswise but whether this would be sufl&cient 

 to overcome the increased resistance it is impossible to determine 

 without knowing the viscosity of endosarc and ectosarc. But 

 without morphological evidence to the contrary we may safely 

 assume the endosarc to be without a fixed structure. 



To eliminate the hydrostatic effect I took advantage of the 

 reaction of the Amoeba which removes a strongly stimulated area 

 from the source of the stimulus. Ordinarily this is done by local 

 contraction of the ectosarc in the region stimulated. However, 

 if this area is in the middle of a flat side, such a contraction is of 

 no avail and I have observed none. Furthermore, if the opposite 

 point of the Amoeba is in contact with the substratum, its con- 

 traction would not aid in the removal of the stimulated point. By 

 studying Amoebae both from the side after the method of Del- 

 linger and from above, I learned to distinguish from above those 



