54 Structure and Classification of Micro-organisms 



others, seen in ameba and in the ciliata, are large, per- 

 manent, and characterized by rhythmical contractions 

 through which they disappear from one part of the body sub- 

 stance to appear in another. These are known as " con- 

 tractile vacuoles," and are supposed to subserve the useful 

 purpose of assisting in maintaining cytoplasttiic currents and 

 so distributing the nourishing juices. 



The cytoplasm also contains remnants of undigested or 

 indigestible foods which constitute the paraplasm or deutero- 

 plasm. In a few cases granules of chlorophyl are also to 



Fig. 15. Internal parasites: A, Amoeba coli, Losch; B, Monocystis 

 agilis, I^euck., a gregarine; C, Megastoma entericum, Grassi, a" flagel- 

 late; D, Balantidium coli, Ehr., a ciliate. 



be found in organisms otherwise resembling animals too 

 closely to be confused with plants. 



The cytoplasm may be soft and uniform in quality, or 

 there may be a surface differentiation into ectosarc, or body 

 covering, and endosarc, body substance. In the rhizopoda 

 there is little difference between the two, though certain 

 fresh-water ameba cover themselves with minute grains of 

 mineral substance, but in most of the mastigophora and in- 

 fusoria corticata the ectosarc is characterized by a peculiar 

 rigidity that gives the animal a definite and permanent form. 

 From the surface covering or ectosarc coarse threads or fine 

 hair-like appendages flagella and cilia often project. In 

 many of the infusoria the ectosarc contains trichocysts from 

 which nettling or stinging threads are thrown out when the 

 organisms are irritated. 



