ENCYSTED STATE OF AMCEBA. 



161 



an equally primitive fashion, usually at some point near the 

 "posterior " end. Besides solid food-stuffs Amoeba takes in a 

 certain quantity of water (along with minute quantities of inor- 

 ganic salts dissolved in it), and it also breathes, by taking in 

 (mainly by diffusion) the free oxygen dissolved in the water and 

 giving off carbon dioxide. 



Such is Amoeba in its active phase. The quiescent or en- 

 cysted state is entered upon under conditions not thoroughly 

 understood, but probably of an unfavorable nature, such as the 



D C 



FIG. 85. A, Amoeba dividing by fission, nucleus not seen (after Leidy). C, Arnreba 

 after a full meal consisting of a large diatom (ilt). (After Leidy). Letters as in 

 Fig. 84. D, Encysted Amoeba, containing food-matters (after Howes). 



lack of food, drying up of ponds, and the like. The pseudo- 

 podia are withdrawn, movement ceases, the body becomes 

 spherical and surrounds itself with a tough membrane (cell-wall) 

 (Fig. 85, D). The animal takes no food and all of its activities 

 are nearly suspended. It is like an animal asleep or hibernating, 

 and in this state it may long remain. Protected by its mem- 

 brane it is able to resist desiccation, and upon the evaporation of 

 the surrounding water it may, as a particle of ' ' dust, ' ' be trans- 

 ported by the winds, even to a great distance. When again 

 placed under favorable conditions the protoplasm bursts its 

 envelope, crawls forth from it, and reassumes its active phase. 



