8o The Insides and the Wordings of Living Things 



order to be alive, that a plant or an animal have the special 

 organs with which we are familiar in ourselves. The simplest 

 plants and animals have indeed no such special organs. 



The simplest animals which we know consist of minute, 

 shapeless lumps of what looks (under the microscope) like 

 colorless jelly, or very fine froth (Fig. i6). Animals of this 



type live in water (or perhaps in 

 the fluids of the body of some 

 larger animal) , and are found in 

 all parts of the world. The ameba 

 moves by protruding the jelly-like 

 mass in one or in several directions, 

 and then flowing into one of the 

 protrusions. When it comes in 

 contact with a solid particle, as a 

 grain of sand, it withdraws this 

 " false foot " and flows off to one 

 side or the other. When it comes 

 in contact with a solid particle 

 that may serve as food, the jelly 

 mass moves forward and envelops 

 the object. Inside the body of the 

 ameba this particle appears to be 

 digested — that is, changed into 

 chemical combinations that can be 

 utilized by the living matter. The 

 solid, undigested remains are re- 

 moved by reversing the process of 

 swallowing — that is, the ameba 

 flows away from the refuse. The 

 surface of the ameba absorbs oxy- 

 gen from the surrounding water, 

 and after portions of the material in the jelly are oxidized or 

 " burned," the products of combustion are discharged by 

 diffusing through to the outside. 



It may be easily shown that the ameba is influenced by 

 contact, by light, by heat, by electric shock, and by chemi- 

 cal shock. In response to a stimulation the shapeless jelly-like 



Fig. 



1 6. The One-celled 

 Animal, Ameba 



When this shapeless mass of jelly- 

 like protoplasm attains its full size 

 the nucleus or kernel lengthens out 

 and gradually divides into two 

 parts. The rest of the animal's body 

 also elongates and the two ends 

 seem to move slowly away from each 

 other until there are two distinct 

 individuals. Each of these is as 

 complete as the other, and both are 

 the same as the mother cell, except 

 for size. From Gruenberg, Biology 

 and Human Life, published by 

 Ginn & Company. 



