126 THE SENSES OF ANIMALS 



the body flows ; when it meets with a minute plant or frag- 

 ment of debris fit for food it pushes out two lobes to surround 

 the particle, and the lobes then flow together so that the 

 food is engulfed in the body where it is digested. Amoeba 

 does not blunder blindly about its environment; when it 

 touches an object it avoids it if it is inedible, but engulfs it 

 if it is suitable food ; it moves towards a smell or taste dif- 

 fused into the water by food, and away from the taint of 

 anything harmful. It moves from darkness into light but 

 retreats if the light is too bright, it moves from temperatures^ 

 that are too hot or too cold, and it reacts to gravity. Thus 

 although Amoeba has no sense organs as we know them — 

 no eyes, ears, nose, or tongue — it reacts to stimuli from the 

 environment in a way similar to that of more complex 

 animals that have those organs. The ability to make these 

 responses must therefore be a property of the living matter, 

 the protoplasm, that makes up the body of Amoeba — and of 

 all other animals. 



The reactions of Amoeba, however, do not imply that it 

 sees, tastes, or feels consciously as we do, any more than a 

 cell in one of our muscles knows that it has been stimulated 

 when it contracts in response to stimulation — we may or 

 may not know that the muscle is stimulated, but the cells 

 of which it consists certainly do not. The single blob of 

 protoplasm that makes up the Amoeba is able to react to 

 many different sorts of stimuli, but in the more complex 

 animals, that consist of numerous cells, more precise reactions 

 are possible where the cells specialize on different single 

 functions — each has its own job to do and is not concerned 

 with anything else. Even in the Protozoa there is an analogous 

 specialization. 



Amoeba is structurally a simple type, but many of the other 

 Protozoa are much more elaborate and have a definite shape, 

 front and rear ends, and gullets for taking in food particles ; 

 they swim by the lashing of innumerable hair-like cilia all 

 over the surface of the body, or by means of a whip-like^a^^/- 

 lum at one end. The soft bodies of some are supported by 

 minute skeletons of silica, or by calcareous shells, which are 

 objects of great beauty under the microscope. There is, too, a 

 dark-coloured spot, usually deep red, in a definite position in 



