MORPHOLOGY AND TAXONOMY OF THE SARCODINA 455 



flagella are permanent structures of the organism, we include as 

 rhizopods those forms with pseudopodia and temporary flagella; 

 flagella and pseudopodia being more or less interchangeable. These 

 are included here in the family Bistadiidae of Doflein. 



Order 1. Amoebida (Gymnamoebida) Ehrenberg. 



Naked forms of Amoebaea, either free-living or parasitic; with one 

 or more nuclei; with contractile vacuole (except in some of the para- 

 sitic forms); reproduction by binary fission, multiple division 

 occasional. Encystment widespread. 



We recognize four families in this order, viz.: Bistadiidae, Amoe- 

 bidae, Endamoebidae and Paramoebidae. Separation of the para- 

 sitic forms of amebae from free-living forms is hardly justifiable 

 in a natural classification but is tolerated on grounds of expediency. 



Family 1. Bistadiidae Doflein.— Organisms characterized by two 

 interchangeable phases — ameboid and flagellated. In the former 

 phase the body is ameboid with lobose pseudopodia. A single 

 nucleus with endobasal body is present; the basal body of the 

 flagellum is formed by division of the endobasal body (Wilson, 

 Puschkarew, et al.) and the flagellum grows out from the basal body. 

 (See Fig. 13, p. 34.) Transformation from the ameboid to the flagel- 

 lated condition involves loss of ameboid movement and change in 

 form to a monaxonic ellipsoidal form. Absorption of the flagellum 

 accompanies transformation again to the ameboid condition. These 

 changes are evidently induced by environmental conditions and, in 

 cultural forms, may be brought about at will. Genera with one, 

 two and three flagella in the flagellate phase are known. Repro- 

 duction by division is limited to the ameboid phase, sexual processes 

 unknown. The ameboid phase is represented by small creeping 

 amebae which have been generally included as Amoeba Umax, and 

 known as "limax" forms. These were separated from the genus 

 Ameba by Chatton and Lalung-Bonnaire (1912) under the name 

 Vahlkampfia. The forms with a single flagellum in the flagellated 

 stage are retained under the generic name Vahlkampfia, although 

 it is by no means assured that all "limax" amebae are thus di- 

 morphic. Forms with two flagella are grouped in the genus D'nnas- 

 tigamoeba Alexeieff and forms with three flagella in the genus 

 Trimastigamoeba Whitmore. Parasitic forms, regarded by Craig 

 (1906) as a cause of human dysentery and with a flagellated phase 

 with one flagellum, are included in the genus Craigia. 



Family 2. Amoebidae (authors generally: em. Doflein, em. 

 Calkins).— The usual types of free-living amebae are grouped in 

 this family. Flagella, so far as known, are absent in all stages. 

 Nuclei single, double or multiple; contractile vacuole usually single, 

 present generally in fresh water forms. Reproduction is by simple 



