A. Porter 
35 
rapidly becomes oval again. As the medium in which the organism is 
being examined under the microscope gradually becomes denser, thus 
placing the Amoeba in an unfavourable environment, the movements 
slow, the organism ceases to form pseudopodia, and encystment ensues 
(Figs. 18—21). I have watched the whole process of encystment 
proceed on a slide under the microscope. 
Movements. 
The movements of Amoeba chironomi are active, a somewhat 
unusual occurrence among organisms of this class. Continuous pro¬ 
gression in one direction may take place, or reversal of the direction of 
Fig. 9. Organism extended and very much flattened. 
Fig. 10. New pseudopodium protruded in a forward direction. 
Fig. 11. Direction of motion reversed. A backwardly directed filopodium now present. 
Figs. 12, 13, 14. Successive reversals of direction of movement. 
Fig. 15. Formation of large backwardly directed pseudopodium before previous one 
(forwardly directed) is completely withdrawn. Beginning of further reversal of 
direction of motion. Cf. Fig. 2. 
3—2 
