232 LIFE : OUTLINES OE GENERAL BIOLOGY 



It seems to flow along or glide along, doubtless in some way gripping 

 the substratum, but attentive observation shows that, at times at 

 least, it is rolling along. For a definitely recognisable particle can 

 be traced moving along the upper surface in the direction in which 

 the Amoeba is going, then disappearing over the front and. after a 

 while, reappearing at the posterior end. There seems to be a "tank"- 

 like or "caterpillar-wheel "-like movement. 



The Amceba is anything but homogeneous; it is not like a drop 

 of white of egg; it has zones in its living matter; it has a nucleus, 

 contractile vacuoles, food-vacuoles and inclusions. It is a little 



Fig. 42. 



Diagram of a Common Amoeba, about a hundredth of an inch in diameter. 

 After Carter. N, nucleus with chromatin spherules; PS, pseudopodium ; 

 D, an engulfed diatom; EN, endoplasm or inner cytoplasm; EC, ecto- 

 plasm or outer zone of cytoplasm; FV, food-vacuoles; CV, a contractile 

 vacuole. 



world "dcr kleine Proteus"; and Prof. A. A. Schaeffer of the Univer- 

 sity of Kansas, who has been for many years a devoted student of 

 amaboid movement, has been able to demonstrate an extremely 

 thin outer fluid layer on the Amoeba, a "plasma membrane" distinct 

 from and external to the familiar outer zone or ectoplasm. Particles 

 adhering to the plasma membrane may be seen moving forwards 

 three to five times as fast as the Ama-ba itself. This extremely 

 delicate plasma membrane is continually giving way at the anterior 

 end of the Amoeba, and being reinstated at the posterior end. It is 

 probably the seat of surface-tension effects, and the tension seems 

 to increase anteriorly and decrease posteriorly. 



