PROTOZOA 69 



Naegleria (Fig. 53). Small amoebae which live in various foul in- 

 fusions ; possess a contractile vacuole ; and in certain conditions pass 

 into a biflagellate phase. Naegleria is placed here rather than among 

 the Rhizomastigina because it is most often in the non-flagellate con- 

 dition, its flagellate phase, though fully grown, is not known to per- 

 form reproduction, and the general features of the amoeboid phase 

 are those of the amoebina of the Umax group, most of whose members 

 appear to have no flagellate phase. These organisms form one or two 



_ fcon.vac. 



Fig. 53. Naegleria bistadialis, X 800. Partly after Kiihn, in Doflein. A, 

 Amoeboid condition. B, Transition to flagellate condition. C, Flagellate 

 condition, coti.vac. contractile vacuole; rh. rhizoplast. 



broad pseudopodia, are given to assuming a slug-like shape with one 

 pseudopodium at the foremost end, and have a very simple nucleus 

 with a large karyosome. 



Vahlkampfia, also found in foul infusions, is a typical member of 

 the Umax group. 



Amoeba (Fig. 54). Typical amoebae, with numerous pseudopodia; 

 contractile vacuole; and no flagellate phase. Various species, of which 

 the commonest three are shown in the figure. The true A. proteus is 

 the largest of the common Amoebae, has a lens-shaped nucleus and 



