310 



APPLIED BIOLOGY 



FIG. 93. Diagrams showing division of an amoeba 

 into two. n, nucleus ; v, vacuole. 



and when the amoeba moves the particles being digested are 

 circulated so that dissolved food is widely distributed. In- 

 digestible particles (hard parts of small animals and cell-walls 

 of plants) are from time to time ejected ; the protoplasm of 

 the amoeba appears to flow away from them as water on a 

 board might for a time surround and inclose some grains of 

 sand and then flow away and leave them behind. 



Respiration. Amoeba breathes like a paramecium; that 



is, simply ab- 

 sorbs oxygen 

 from the sur- 

 rounding water. 

 Excretion is 

 the same as in 

 a paramecium; 

 carbon dioxide 

 is absorbed by 

 the surrounding 



water, and water and nitrogenous excretions are pumped 

 out by the contractile vacuole. 



Reproduction. Amcebas are rarely seen dividing, but if 

 kept in watch-crystals they multiply rapidly, making it 

 evident that they must undergo division frequently. Figure 

 93 shows the process of division. Conjugation of two amoebas 

 similar to that of the paramecium ( 267) has been seen. 

 Under conditions unfavorable to the usual activity, amoebas 

 will sometimes become rounded, and secrete around them- 

 selves a hard wall or cyst. They are said to be encysted. In 

 this condition they are able to live for some time without 

 food and in a dry state. Such a habit insures their existence 

 in dry seasons when the ponds are dry. Also, in the dry 

 condition they may be widely scattered by winds. 



271. Simple Life of Amoeba. Compared with the para- 

 mecium, the amoeba is exceedingly simple in structure and 

 functions. The paramecium has a constant and definite 



