CHAPTER LV 

 CLASS I SARCODINA (RHIZOPODA) 



THE AMEB2E 



These organisms belong to the order Amebina (Ehrenberg). They 

 are characterized during the vegetative stage by a semifluid consis- 

 tence, permitting rapid changes of form, ameboid 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 takes place by the 

 conjugation of two merozoites and 'possibly by autogamy. 



Since some flagellates possess an ameboid 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 amebag, including all the parasitic forms 

 (endamebse), possess a single nucleus, yet Ameba diploidea and Ameba 

 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 hyaline ectoplasm, the latter forming the pseu- 

 dopods by which the animal moves from place to place. 



Until recent years all ameboid organisms were placed in the genus 

 Ameba, but Schaudinn revived a genus originated by Leidy of Phila- 

 delphia, the Endameba, 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 Ameba 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 amebae is of some interest, because of the con- 

 fusion they have caused in the study of parasitic ameba ; they are the 

 so-called "limax amebae, " which have been cultivated on agar, and 

 for this genus Chatton (1912) has proposed the name Vahlkampfia. 

 They are small organisms, 5 to 30 microns in diameter, provided with 



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