442 BIOLOGY OF THE PROTOZOA 



of the radiolarian, but as swarmers of parasitic dinoflagellates 

 (Merodinium). Such problems remain unsolved until the full 

 development of the swarmers is observed. 



We offer no apology for not attempting a special classification 

 of this group or a key to the genera. The enormous number of 

 genera of Radiolaria require monographic treatment which may be 

 found in Haeckel's three volumes of Challenger Reports and in 

 Schewiakoff's monograph of the Acantharia {Fauna and Flora, 

 Golfes von Xeapel, vol. 37, 1926). 



Class II. RHIZOPODA von Siebold. 



With the Rhizopoda we find types of derived organization that 

 are not found in the Actinopoda. Myxopodia, filopodia and lobo- 

 podia are characteristic, although rarely combined in the same indi- 

 vidual. The protoplasm is generally alveolar and may or may not 

 be differentiated into distinct ectoplasm and endoplasm but in gen- 

 eral shows less differentiation than in ciliates or flagellates or even 

 in Actinopoda. Protoplasmic inclusions, of the nature of metaplas- 

 tids, are highly varied while definite plastids are rare. A single 

 chloroplastid of unknown significance, in the form of a blue-green 

 so-called chromatophore, is present in the testate rhizopod Pauiin- 

 ella but these are not known elsewhere in the group. Pascher 

 (1929) finds that these " chromatophores " of Paulinella are able to 

 live independently of the rhizopod and he regards them as a distinct 

 genus of blue-green algae. Metaplastids such as " chromatoid bod- 

 ies" are characteristic of the parasitic amebae (Endamebidae), 

 while fat and glycogen-like bodies are widely distributed. These 

 are particularly abundant in the fresh water species Pelomyxa 

 palustris Green", the highly refringent bodies " Glanzkorper " found 

 here in abundance are interpreted by Stole and Bott as glycogen- 

 like in composition, by Veley (1905) as albuminous, and by Gold- 

 schmidt (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 (Clado- 

 thrix pelomyxae Veley) is still a matter of hypothesis. Chromidia, 

 or cytoplasmic chromatin granules, arc characteristic and may be 

 permanent or periodic constituents of the cytoplasm (see p. 69). 



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 {e. g., Cochliopodium bilimbosum) while the great 

 majority of Rhizopoda have tests of pseudochitin on which mineral 

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

 aminifera, calcium carbonate is precipitated between two such 

 membranes of chitin, resulting in the highly complex and multiform 

 shells of lime stone. 



