PROTOZOA 



131 



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though the organisms mentioned in this classification are placed in 

 the position usually given to them, it must be understood that this 

 classification is not final, and that the discovery of new stages in the 

 life history of some of these protozoa may make it necessary to remove 

 them from the classes in which they have been placed. For example, 

 before its flagellate stage was known, 

 Leiskmania donovani was classified with 

 the sporozoa; now it is grouped with the 

 herpetomonads. 



The characteristics of the different 

 genera and of the unimportant parasites 

 are very briefly mentioned in the follow- 

 ing paragraphs; the important parasites 

 are treated more fully in the pages indi- 

 cated by the references given, in brackets, 

 throughout the classification. 



The RHIZOPODA include the simplest 

 forms of animal life. A rhizopod, such 

 as an amoeba, consists of a single cell, 

 without a protective covering, and with- 

 out permanent organs of locomotion; it 

 moves about and captures its food 

 through the agency of its pseudopodia. 

 Very few of the rhizopods are parasitic; 

 most of those whiph are parasitic, belong 

 to the genus Eniamosba. Different 

 species of parasitic amoebae may occur 

 in the alimei^tary canals of various ani- 

 mals. Certain of these produce serious 

 diseases (page 822). 



The FLAGELLATA are distinguished 

 by possessing one or more flagella; 

 they often have, also, a fin-like, undulating membrane extending 

 along the surface of their body. Many possess two nuclei, a larger 

 trophonucleus which has to do with nutrition and a smaller kineto- 

 nucleus which is intimately connected with the organs of locomo- 

 tion. This group has thus been termed the Binucleata by certain 

 systematists. Most flagellates are free-living. Comparatively few 



Fig. 94. — H erpetomonas 

 musciB-domesticcs (Burnett). A, 

 motile individual with two flag- 

 ella; B, cyst; «, nucleus; hi,' 

 kineotonucleus. {After Pro- 

 ■wazekfrom Minchin.) 



