74 



Elementary Biology. 



whereby the water, and possibly also certain nitrogenous 

 excreta, are separated from the protoplasm and ejected on 

 the surface. The general physiology of Amoeba^ the effect 

 of the application of heat, &c., has been already described 

 fully above (pp. 33-35). 



At a certain period at present, so far as we know, unde- 

 terminable, but probably in some way related to the condi- 

 tion of the environment and the state of nutrition of the 



FIG. 18. Amoeba polypodia (Max Schultze.) 



, nucleus ; '/Y, contractile vacuole, 



animal itself the Amoeba assumes a more or less globular 

 form and becomes enclosed in a cellulose cyst. No seg- 

 mentation, however, takes place as in Protomyxa. After 

 a period of a few hours the cyst bursts and the Amoeba 

 escapes and becomes actively motile. This process is 

 known as rejuvenescence. 



Amoebae are inhabitants of damp earth and stagnant 

 water, and are decidedly local in their distribution, as might 

 be expected from the absence of special possibilities for 

 diffusion. They vary much in size, but a common size is 

 from T -^o7) tn to Tou tn f an mcn - Vegetative multiplication 



