CHAPTER LIV 



CLASS I SARCODINA (RHIZOPODA) 

 THE AMOEBA 



THESE organisms belong to the order Amcebina (Ehrenberg). They 

 are characterized during the vegetative stage by a semifluid consist- 

 ence, permitting rapid changes of form, amoeboid movements, and 

 progression by means of pseudopods. There is no internal skeleton 

 and the protoplasm is naked and may be differentiated into endo- and 

 ectoplasm, and in some cases a contractile vacuole is present. All 

 forms possess one or more nuclei. Multiplication takes place by divi- 

 sion into two or more daughter cells. Fertilization possibly takes place 

 by the conjugation of two gametes. . 



Since some flagellates possess an amoeboid stage, it is necessary to 

 know most of the life cycle of an organism before classifying it as an 

 ameba. The protoplasm varies greatly in its consistency, depending 

 on the species as well as the stage of the life cycle, and the environ- 

 ment and food supply. Most amoeba, including all the parasitic forms 

 (entamoebae), possess a single nucleus, yet Amoeba diploidea and Amoeba 

 binucleata always have two, and the other species may show more. 

 The nucleus of all types possesses a karyosome. The nucleus is well 

 developed and in it may be followed either a simple or typical mitosis. 

 The cytoplasm is usually at some stage divided into a granular endo- 

 plasm and a clear or hyalin ectoplasm, the latter forming the pseu- 

 dopods by which the animal moves from place to place. 



Until recent years all amoeboid organisms were placed in the genus 

 Amoeba, but Schaudinn established a genus, the Entamoeba, for the 

 parasitic species which have many points of difference from the free 

 living varieties. Of the free living forms, the easiest to study is the 

 Amoeba proteus (Pallas), a very large organism, 200 microns in 

 diameter, found frequently in stagnant water; it, however, has no 

 direct importance in medicine. Another group of free living amoeba) 

 is of some interest, because of the confusion they have caused in 

 the study of parasitic amoeba; they are the so-called "limax amcrbse," 



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