456 BIOLOGY OF THE PROTOZOA 



division in vegetative forms, by multiple division during quiescent 

 phases. The great majority of forms are aquatic and developmental 

 phases of other types (e. g., mycetozoa) may be easily mistaken for 

 amebae. Others are semi-terrestrial, living in damp earth, moss, 

 etc., where they play a part in keeping down bacteria of the soil 

 (see Goodey). 



Family 3. Endamoebidae.— These are parasitic amebae widely 

 distributed throughout the animal kingdom and with characteris- 

 tic vegetative phases during which the organisms live as harmless 

 commensals or, more rarely, as pathogenic parasites in the host, 

 and with permanent cyst stages by which infection is carried by 

 means of contaminative infection. The genus generally recognized, 

 Endamoeba, is represented by a vast number of species with ill- 

 defined diagnostic characters, while many questionable genera are 

 forms about which the taxonomic position is still in dispute (see 

 Chapter X). Nutrition is either holozoic, saprozoic or heterozoic. 



Family 4. Paramoebidae. — Forms with single nucleus and pecu- 

 liar cytoplasmic structure (Nebenkern) variously interpreted as a 

 kinetic element, intracellular parasite, etc. Both free-living and 

 parasitic species. Genus: Paramoeba. 



Order 2. Testacea. 



These forms are generally described as amebae with shells; by 

 some they are grouped as a subdivision of the Foraminifera (Doflein). 

 The protoplasmic and test structure, as well as the pseudopodia 

 are so different from Foraminifera that little is gained by this pro- 

 cedure, while the association with naked forms has a long historical 

 backing. They are almost exclusively fresh water forms, although 

 some species are represented in brackish water as well. Many 

 species are semi-terrestrial and abound in moss and similar damp 

 places. The protoplasmic body differs from that of the Amoebidae 

 in having the ectoplasm concentrated at the region of the shell 

 opening, while many forms show a distinct zonal differentiation of 

 the protoplasm. Contractile vacuoles are always present. 



Nuclei are either single, double or multiple and are usually accom- 

 panied by a zone of chromidia in the form of a dense reticulum 

 from which, according to the observations of numerous observers, 

 the nuclei of gametes are formed (Schaudinn, Zuelzer, Elpatiewsky, 

 el al.). It is rather the fashion to doubt this interpretation on the 

 ground that such nuclei are possible parasites, but we shall adhere 

 to it until the critics have a more probable explanation of the 

 nature of the chromidia (p. 69). 



Pseudopodia are filopodia which in a few instances have the 

 tendency to branch (Fig. 18S). They lack the medullary endoplasm 

 of lobopodia and have a considerable power of independent move- 



