472 



PROTOZOA 



The Flagellata 1 are organisms composed of naked, variously constructed 

 protoplasm, and moving by means of one or more long flagella. Some 

 forms also show amoeboid movements. The number and characteristics 

 of the flagella vary. Generally there is a principal flagellum directed for- 

 ward, and there are from one to several flagella directed backward. Often 

 a flagellum seems to be attached throughout part of its length to the body 

 of the organism by a wavy or undulating membrane. The protoplasm of 

 the flagella appears homogeneous, except for the fact that it may occasion- 

 ally show small granules. The flagella arise from small granules, the " fla- 

 gella roots," which, according to some authors, are similar to centrosomes, 

 and, according to others, micronuclei. The body of the flagellata is gen- 

 erally round or oval and more or less motile. Its protoplasm may be finely 

 or coarsely granular, sometimes reticular, and may contain one or more 

 vacuoles, one or two of which, situated anteriorly, may be contractile. It 



FIG. 141 



Two cells infiltrated with spores of the plasmodiophora brassicee. (Doflein.) 



may also contain various food particles. The nucleus situated anteriorly 

 varies in appearance in the different species. It is usually more or less 

 granular, with a central body, but in some species it is vesicular. The 

 flagellata multiply either in the purely motile condition or after encysting. 

 In the first case the division is generally longitudinal. In the second case 

 they may or may not conjugate before they encyst. Then division forms 

 occur in the cyst by a process somewhat similar to that in the aincebse. 



Flagellates are found in foul and stagnant water, in the ocean, 

 and a few in rivers and in the body fluids of higher animals. The fol- 

 lowing species which are described below have been reported as being 

 parasitic in man: trypanosoma, cercomonas, trichomonas, lamblia 

 intestinalis. 



The sporozoa are a group of exclusively parasitic protozoa of very 

 widespread occurrence, living in the cells, tissues, and cavities of ani- 



1 See Figs. 146 and 147, under trypanosoma Lewisi. 



