No. 4S3-] 



ACTIVITIES OF AMG-IBA. 



Neither theoretically nor practically does there api)ear to 

 evidence that movements due to changes in surface tens' 

 take place without these characteristic currents. We cam 

 consider the movements of Amteba to be due to a tlccr 

 surface tension at the anterior end, as in the "imitatioi- 

 precisely the feature which led to the supposition that tlv 

 ments in the two cases were of the same character we fi" 

 there is actually an absolute contrast. In Amceba the 

 currents are in the direction of movement of the mass, an 

 same direction as the central current ; in the imitatio 

 are in the opposite direction. 



Clearly the surface tension theory will not account 

 phenomena as they actually exist. This becomes still m 

 dent when we consider the formation of pseudopodia 

 contact. In these there is not only no backward curr- 

 also no resting surface ; axis and surface move outwarc 

 same direction as the tip. Such movements are not pr< 

 by local changes in surface tension. The " imitations 

 tations only to the extent that they are fluids and that tiie\ 

 they are not imitations so far as the nature of the mu\ 

 and their cause is concerned. 



A much more nearly accurate imitation of tlic movx-n- 

 Amoeba may be produced with gravity as tin: active v,- 

 place of surface tension. A drop ot watL-r moving dowi- 

 a surface to which it does not cling strongly .sIk.wsUv 

 rolling movement that we find in Amoiba, I lie lowei 

 (in contact with the substratum) i> at re>i. vnIhK: llu- i;p 

 face moves forward and passes continual]} around the : 

 end to the lower surface. But we know th it gra\iiy i> 

 active agent in the movement of Amo ha. 



An imitation of the usual locomotion of .Xmo-ba thai 

 rate even to minute details is described In ihc present ai 

 the paper on the behavior of Ani(el)a already citc<l (]'■ 

 : 04). A drop of fluid resting on a >ub^tratum i> ca 

 adhere to the substratum more strongly at one ed-e tha 

 other. Thereupon the drop moves toward the more a 

 edge, and in so doing it shows exactly the form and mo 

 of an Amoiba in locomotion. The experiments may 



