SPECIAL MORPHOLOGY AND TAXONOMY OF SARCODINA 323 



thin, hut later shown by Biitschh to be composed of strontium 

 sulphate; (3) NasseUaria, with skeletons and spicules of silica; and 

 (4) PhoBodaria from the presence of a pigmented mass or phseodium, 

 around the opening of the primary astropyle (see Key, p. 343 for 

 classification). 



Class II. RHIZOPODA, von Siebold. 



With the Rhizopoda we find many more types of structure than 

 are found in the Actinopoda. ]Myxopodia, filopodia and lobopodia 

 are characteristic but are rarely combined in the same individual. 

 The protoplasm is generally alveolar and may or may not be differ- 

 entiated into distinct ectoplasm and endoplasm but in general shows 

 less differentiation than in ciliates or flagellates or even in Actino- 

 poda. Protoplasmic inclusions, of the nature of metaplastids, are 

 highly varied while definite plastids are rare. A single chloroplastid 

 in the form of a blue-green chromatophore is present in the testate 

 rhizopod PaidineUa but these are not known elsewhere in the group. 

 Metaplastids such as "chromatoid bodies" are characteristic of the 

 parasitic amoebae (Endamoebidfe), while fat and glycogen-like bodies 

 are widely distributed. These are particularly abundant in the 

 fresh-water species Pelomyxa pahisiris, Greeff, the highly refringent 

 bodies " Glanzkorper" found here in abundance are interpreted by 

 Stol^ and Bott as glycogen-like in composition, by Veley (1905) as 

 albuminous, and by Goldschmidt (1904) as the plastin remains of 

 nuclei which have broken down with the formation of chromidia. 

 The function of these inclusions and of the accompanying bacteria- 

 like organisms (Cladothrix yelomyxoB, Veley) is still a matter of 

 hypothesis. Chromidia, or cytoplasmic chromatin granules, are 

 characteristic and may be permanent constituents of the cytoplasm 

 or periodic (see p. 48). 



Living membranes equivalent to the cortical membranes of 

 flagellates, ciliates and gregarines are rarely found here. Transi- 

 tions toward the chitinous and pseudochitinous tests are present in 

 some forms ie. cj., CochUopodimn hilimhcsnm) while the great 

 majority of Rhizopoda have tests of pseudochitin on which mineral 

 substances of quartz, silica, or other types, are cemented. In 

 Foraminifera, calcium carbonate is precipitated between two such 

 membranes of chitin, resulting in the highly complex and multiform 

 shells of lime stone. 



Contractile vacuoles are present in fresh-water forms but are 

 generally absent in marine t^7)es. They never have the complex 

 canal system such as found in some flagellates and ciliates and are 

 rarely fixed in position. Gas vacuoles are present in some of the 

 testate fresh-water forms {ArccUa). 



The majority of Rhizopoda are multinucleate both in fresh water 



