bl 



134 MORPHOLOGY AND CULTURE OF MICROORGANISMS 



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 protozea may make it necessary to remove 

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



before its flagellate stage was known, 

 Leishmania 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. 

 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 which are parasitic, belong 

 to the genus Entamoeba. Different 

 species of parasitic amoebae may occur 

 in the alimentary canals of various ani- 

 mals. Certain of these produce serious 

 diseases (page 876). 



The FLAGELLATA are distinguished 

 by possessing one or more flagella; 

 they often have, also, a fin-like, un- 

 dulating membrane extending along the surface of their body. 

 Many possess two nuclei, a larger trophonucleus which has to do 

 with nutrition and a smaller kinetonucleus which is intimately 

 connected with the organs of locomotion. This group has been 

 termed the Binudeata by certain systematists. Most flagellates are 

 free-living. Comparatively few species are parasitic, but some of 

 these cause very serious diseases (page 879). 



FIG. 95. Herpetomonas 

 musca-domestica (Burnett). A, 

 Motile individual with two flag- 

 ella; B, cyst; , nucleus; bl, 

 kinetonucleus. (After Pro- 

 wazekfrom Minchin.) 



