MOVEMENTS 2Q 



The plasmalemma, which is sticky, adheres to the ground where 

 it is in contact, so that the effect of the forward thrusting of the 

 protoplasm within is to roll it along, as an india-rubber bag 

 filled with water may be rolled over a surface, and thus the 

 animal travels in the direction of the thrust. Those pseudopodia 

 of A. protetis which do not touch the ground merely protrude 

 without causing locomotion, but the creature may place their 

 tips upon the ground and thus walk upon them. When it is 

 floating freely it puts out slender, finger-like pseudopodia and 

 appears to be searching with them for foothold. During the 

 movements the contents of the endoplasm — nucleus, food 

 particles, etc. — are carried about freely from place to place in the 

 body, but the contractile vacuole adheres to the inner surface of 

 the ectoplasm and moves with it. 



NUTRITION 



Amceba feeds on small organisms, which it ingests by surround- 

 ing them, together with a drop of water, with outgrowths of its 

 protoplasm and so engulfing them. The space in the body which 

 the prey comes to fill would thus be lined with ectoplasm, but the 

 ectoplasm here becomes absorbed into the surrounding endoplasm, 

 so that it is clear that there is no essential difference between 

 the m^aterials which compose these layers. There are then secreted 

 around the food particle substances which kill it and digest its 

 nourishing part. The space containing the digestive juice is known 

 as a food vacuole, and its reaction while digestion is going on is 

 acid. The chief food of Amceba is protein, but A. proteus and other 

 species can digest fat. Their ability to deal with carbohydrate is 

 doubtful. The dissolved substances are incorporated, and the 

 undigested parts are egested by the simple process of being left 

 behind as the animal flows along. Different species have different 

 food preferences and Amceba proteus does not feed on diatoms but 

 can survive indefinitely on the small ciliate Colpidium, which is 

 found in infusions in association with Paramecmm (p. 46). 



IRRITABILITY, AUTOMATISM AND CONDUCTIVITY 



The protoplasm of Amoeba is irritable, automatic, and con- 

 ductive. Its irritability is not, as in higher animals, localised in 

 sense organs, but that this property exists in it is shown in 



