The Protozoa 



47 



filled with endless chambers in which its enzymes and other active 

 substances, etc., are stored up and its functions carried on. 



In addition to these chambers, which are minute and of uniform 

 size, there are larger spaces called vacuoles, some of which are the 

 result of temporary conditions— accumulations of digested but not 

 yet assimilated food, etc.; but others, seen in ameba and in the 

 ciliata, are large, permanent, and characterized by rhythmical 

 contractions through which they disappear from one part of the 

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

 tractile vacuoles," and are supposed to subserve the useful purpose of 

 assisting in maintaining cytoplasmic currents and so distributing the 

 nourishing juices. 



The cytoplasm also contains remnants of undigested or indigest- 

 ible foods which constitute the paraplasm or deuteroplasm. In a 



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

 Leuck., a gregarine; C, Megastoma entericum, Grassi, a flagellate; D, Balantidium 

 coli, Ehr., a ciliate. 



few cases granules of chlorophyl are also to 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 masti- 

 gophora and infusoria 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. 



The body substance may show no morphologic differentiation in 

 rhizopoda, but in the corticata there may not only be a permanent 



