The Sarcodina 241 



may be wide even within a single genus, since different species of Endo- 

 limax have been reported from termites and from primates. Most Enda- 

 moebidae are probably endocommensals, or else approach such a status. 

 However, there are notable exceptions, such as Entamoeba histolytica of 

 man (Chapter XI), and E. invadens which may produce fatal infections 

 in various reptiles (39, 119). As in the case of the Amoebidae, the assign- 

 ment of genera to this family is based upon their sharing a common 

 habitat rather than upon a consideration of more valid taxonomic cri- 

 teria. It is not impossible that some of the Endamoebidae are more closely 

 related to certain free-living amoebae than they are to other members of 

 their own "ecological" family. The following genera have been included 

 in the Endamoebidae: 



Endamoeba Leidy (Fig. 5. 28, E-G), erected for Biitschli's Amoeba blattae (90, 95), 

 contains parasites of cockroaches and termites (49). 



Entamoeba Casagrandi and Barbagallo (Fig. 5. 28, A-C) includes species from the 

 major groups of vertebrates. Although the validity of this generic name, as distinct 

 from Endamoeba Leidy, has been disputed extensively, reasons for retaining Entatnoeba 

 as a generic name for E. coli and related amoebae are ably presented by Kirby (72). 

 This usage emphasizes the fact that E. blattae and E. coli cannot logically be placed 

 in the same genus. The three species parasitic in man are discussed in Clhapter XI. 



EndoUmax Kuenen and Swellengrebel (Fig. 5. 28, D) is represented in termites and 

 cockroaches as well as various \ertebrates. E. nana of man is described in Chapter XI. 



Dientamoeba Jepps and Dobell includes a parasite of the human colon, while 

 lodamoeba Dobell is represented in pigs and in man (Chapter XI). 



Hydramoeba Reynolds and Looper (121, 122; Fig. 5. 28, H) includes a rather large 

 amoeba which attacks the epithelial layers of Hydra, often with fatal results. 



Order 4. Testacida 



These are typically creeping organisms which develop lobopodia 

 or filopodia and possess one-chambered tests. The primitive test is com- 

 posed of an apparently single secreted layer. The material is said to be 

 "pseudochitin" (1). The flexibility of the test in Pamphagus and Cochlio- 

 podimn, for instance, indicates there is no significant addition of inor- 

 ganic material. Mixtures of silica with the basic "chitinous" material are 

 found in relatively firm tests which maintain a characteristic shape, as in 

 Hyalospheiiia. 



The test of most Testacida apparently contains two layers (Fig. 5. 29, 

 J). The inner layer is composed of "chitin," sometimes mixed with sili- 

 ceous material. The structure of the outer layer varies in different genera. 

 Although apparently bivalve in Clypeolina rnarginata (109), this layer 

 seems to be continuous in other Testacida. In Arcella (Fig. 5. 29, C-F), 

 more or less spherical elements are cemented together in a honeycomb 

 pattern. In Amphizonella (Fig. 5. 29, L), the test is sometimes covered 

 with a "gelatinous" layer. Difflugiidae ingest sand grains, and occasionally 

 diatom shells, which are used with little or no modification in construc- 

 tion of the test. Such particles are embedded in a "chitinous" cement. 

 The test of Centropyxis (Fig. 5. 29, K) apparently is constructed of a 



