AMEBOID MOVEMENT 



49 



It is a very simple matter to demonstrate the existence of 

 this layer. Although any insoluble non-toxic substance of low 

 specific gravity such as carmine or soot, "when reduced to very 

 small particles and mixed with the water in which the amebas 

 to be examined live, will cling to the outside of the ameba so that 

 the movement of the outer layer can be observed; in my ex- 

 perience the best as well as the most convenient substance to use 

 is the dried flocculent colloidal sediment from ameba cultures, 

 rubbed to powder with the ball of the finger. This powder 

 swells up in water into flocculent masses which are large for their 

 weight and do not show such active Brownian movement as 

 particles of carmine or india ink, and they consequently adhere 

 more easily to the ameba. Moreover no foreign substances are 

 thereby introduced into the water. 



Of the more common species of amebas, those with the firmer 

 ectoplasms are the most favorable for studying the movements of 

 the outer layer. We may therefore first take up several observa- 

 tions on Amoeba sphaeronucleosus (Figure 13). This ameba re- 



Figure 13. Amoeba sphaeronucleosus. In locomotion. Note the nucleus, 

 contractile vacuole, ectoplasmic ridges. This ameba is not known to form 

 pseudopods. Length, 120 microns. 



sembles the more common A. verrucosa. It is about 120 microns 

 long and is usually of an o-val shape in locomotion. It is more 

 active and less disturbed by jars than verrucosa. 



Figure 14 represents a sphaeronucleosus with a small particle 

 attached to the middle of the upper surface of the ameba. As the 



