PHYLUM PROTOZOA 



35 



potassium bichromate when placed near the mercury produces 

 a solution which causes local lowering of the surface tension of 



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FIG. 12. Locomotion of Amcba pro/ens. Photographs in side view. A 

 and B show a specimen attached at two points, a and b, and a pseudopod which 

 projects from one end and bends down to the substratum as in B at d ; C shows 

 the extension of a long pseudopod. (.From Dellinger in Journ. Exp. Zool.) 



the drop, and results in the formation of projections and move- 

 ment of the mercury in various directions. 



REACTIONS TO STIMULI. -- A turning of an animal resulting 

 from a change in its environment, for example an increase in 

 the intensity of the light, is known as a " tropism" or "taxis.'' 



