30 AMCEBA. PHYLUM PROTOZOA 



various ways. If Amoeba be stimulated by slight contact or by 

 meeting very dilute solutions of various chemical substances 

 it will form a pseudopodium on the side towards the stimulus. If 

 it be pricked with the end of a fine thread of glass, or come into 

 contact with stronger solutions of chemical substances, it will draw 

 back and flow away. In this case the formation of a pseudopodium 

 in a region of the body other than that which has been stimulated 

 shows that the protoplasm has the property of conductivity. 

 Again, it does not swallow every particle it comes across, but 

 chooses those that either contain nourishing substances or are in 

 motion (in which case they are probably alive and therefore fit for 

 food). By an unkind deception of this ' sporting instinct ', it may 

 be induced to capture and swallow moving particles of glass. Its 

 mode of seizing food is not fixed, but adjusted with an uncanny 

 appearance of intelligence to the nature and behaviour of the prey 

 of the moment, which it dogs with perseverance and resourceful 

 changes of method. It wiU move away from strong light, but does 

 not appear to perceive a particle of food better in the light than in 

 the dark. All this shows that it receives from foreign bodies various 

 stimuli, and discriminates between them. In contrast to these 

 instances, many of its actions cannot be traced to any stimulus, 

 and must therefore be classed as automatic in the sense in which 

 that word is used in biology. In much of its activity it appears to 

 be exploring its surroundings and to continue on a course until 

 it receives some stimulus which repels it, but sometimes, as in 

 capturing food, it appears to be attracted in the direction from 

 which a stimulus comes. 



RESPIRATION AND EXCRETION 



Since the peUicle of Amoeba is thin it is probable that liquid 

 and gaseous substances other than those with very large molecules 

 can pass in and out with some ease, and what evidence there is 

 suggests that this is so. Amoeba is known to absorb oxygen, and 

 since there are no special organs for the purpose it must be 

 presumed that the gas diffuses in all over the surface. In the same 

 way, since it is virtually certain that no animal can feed on 

 protein without producing nitrogenous waste products, it must 

 be assumed that these diffuse out. In A. leschercB masses of 

 crystals have been observed to collect in a large vacuole and, 

 after being violently swirled round, to be shot out. These have 



