234 The Sarcodina 



sory pseudopodia which may have httle or no function in locomotion. 

 A hyahne ectoplasm and a granular endoplasm are usually distinguish- 

 able. A flagellate stage has been reported in several species usually 

 assigned to the order; in the rest, the cycle apparently is monomorphic. 

 Many species occur in the digestive tract of invertebrates and vertebrates; 

 others are free-living in fresh and salt water and in the soil. 



The order is often divided into three families: Dimastigamoebidae, 

 in which the life-cycle includes both a flagellate and an amoeboid phase; 

 Amoebidae, free-living species without a flagellate stage; and Endamoe- 

 bidae, the endoparasitic amoebae. 



Family 1. Dimastigamoebidae. The dimorphic cycle includes a domi- 

 nant amoeboid phase and a flagellate phase of relatively short duration. 

 Members of the family have been reported from fresh water and from 

 cultures inoculated with feces of certain insects and of various verte- 

 brates (including man). 



Naegleria griiberi is the best known representative (113, 156, 161). The 

 small amoeboid stage (Fig. 5. 24, A, B, I) commonly forms one large 

 lobopodium. The nucleus contains a large Feulgen-negative endosome 

 which divides in mitosis. The flagellate stage (Fig. 5. 24, C, D, M), which 

 has two equal flagella, is a temporary one under the conditions reported; 

 ingestion of food has been described in only one instance (113). The 

 transformation from amoeba to flagellate is induced by diluting the cul- 

 ture medium with water (113, 161). Cysts (Fig. 5. 24, E-H) are usually 

 but not always uninucleate. The cyst membrane shows two well-defined 

 layers and also several opercula, through one of which the organism 

 emerges during excystment. 



The generic composition of the family has been disputed. The type 

 genus, Dimastigamoeba Blochmann (9), is based on Dimastigamoeba 

 (Dimorpha) radiata (Klebs). The amoeboid phase (73) develops slender 

 radially arranged pseudopodia; the flagellate stage has two unequal flag- 

 ella, one of which is usually trailed. Dimastigamoeba simplex Moroff 

 (Fig. 5. 24, Q) is similar to D. radiata (93). The genus Naegleria Alexeieff 

 em. Calkins (2, 18) includes species with a flagellate stage showing two 

 equal flagella, and an amoeboid stage which moves by means of a blunt 

 lobopodium. There seems to be no sound reason for assuming that 

 Naegleria is a synonym of Dimastigamoeba. The status of Trimastiga- 

 7noeba Whitmore is uncertain, since stages with two, three, and four 

 approximately equal flagella were figured for T. philippinensis (159). 

 Such material might suggest a biflagellate organism in various stages of 

 flagellar duplication prior to fission. Hollande (53) has suggested that 

 Naegleria Alexeieff is a synonym of Vahlkampfia Chatton and Lalung- 

 Bonnaire (Fig. 5. 26, A-F). However, a flagellate stage was not reported 

 in V. punctata (24), and the structure of the dividing nucleus, although 

 similar to it, is not identical with that described for N. griiberi (113). 



