344 



PROTOZOOLOGY 



Family 1 Dimastigamoebidae Wenyon 



The members of the two genera placed in this family possess both 

 amoeboid and flagellate phases {diphasic). In the former, the organ- 

 ism undergoes amoeboid movement by means of lobopodia and in 

 the latter the body is more or less elongated. Binary fission seems to 

 take place during the amoeboid phase only. Thus these are diphasic 

 protozoans, in which the amoeboid stage predominates over the 

 flagellate. The amoeboid phase resembles a 'limax' amoeba; under 

 natural circumstances, it is often exceedingly difficult by observing 

 the amoeboid stage only, to determine whether they belong to this 

 family or the family Amoebidae. 



Fig. 160. a-c, trophozoite, flagellate phase and cj^st (all stained) of 

 Dimastig amoeba gruberi, x750 (Alexeieff); d-f, similar stages of D. 

 bistadialis, X750 (Kiihn); g-j, trophozoite, flagellate phase, cyst and 

 excystation of Trimastigamoeba philippi7iensis X950 (Whitemore). 



Genus Dimastigamoeba Blochmann ( Nacgleria Alexeieff). Minute; 

 flagellate stage with 2 flagella; amoeboid stage resembles Vahlkamp- 

 fia (p. 350), with lobopodia; cytoplasm differentiated; vesicular 

 nucleus with a large endosome; contractile vacuole conspicuous; 

 food vacuoles contain bacteria; cysts uninucleate; free-living in 

 stagnant water and often coprozoic. 



D. gruberi (Schardinger) (Fig. 160, a-c). Amoeboid stage 10-50)u 

 long; cyst wall with several openings; flagellate stage 10-30/i long; 

 stagnant freshwater and often coprozoic. 



D. bistadialis (Puschkarew) (Fig. 160, d-f). Similar in size; but 

 cyst with a smoother wall. 



Genus Trimastigamoeba Wliitmore. Flagellate stage bears 3 

 flagella of nearlj- equal length ; vesicular nucleus with a large endo- 

 some; amoeboid stage small, less than 20m in diameter; uninucleate 

 cysts with smooth wall; stagnant water. One species. 



