288 Descriptive Zoology. 



amoeba. Occasionally a grain of sand, or other indiges- 

 tible matter, is taken in ; in this case it is finally passed 

 out of the body, usually being left behind as the amoeba 

 moves on. There is no mouth ; food may be taken in at 

 any part of the surface. There is no stomach ; the space 

 occupied by the ingested food is an improvised stomach. 

 There is no anus, residual matter being passed out at the 

 point most convenient. Still, as the amoeba moves about 

 in search of food, the surface that happens to be foremost 

 is likely to take in the new matter, and the part that is, 

 for the time, rearmost serves as the place of exit. The 

 amoeba may be said to flow around its food, and to flow 

 away from, and so leave behind, its waste matter. 



The work of moving about involves the expenditure of 

 energy. This energy is produced by the oxidation of the 

 substance constituting the amoeba. Oxygen is constantly 

 being absorbed through the surface to supply this need, 

 which varies according to the degree of activity. The oxi- 

 dation of the matter of the body of the amoeba produces 

 carbon dioxid and water, which are passed off, invisibly, 

 through the surface. The new food taken replaces the loss 

 by such oxidation. This taking in of oxygen and giving 

 out carbon dioxid is respiration, in its simplest form. In 

 the oxidation heat is produced, which probably is given 

 off to the water about as fast as it is produced in excess 

 of the temperature of the surrounding medium. Actively 

 moving amoebae warm the water in which they move, as 

 truly as we warm the water in which we are bathing, 

 or the air in which we are performing active muscular 

 work. And as we taint the air with our waste products 

 and need a constant renewal of the surrounding air, so 

 the amoeba must not be confined too closely in a limited 

 quantity of water that is sealed from the air. 



