MORPHOLOGY AND TAXONOMY OF THE SARCODINA 437 



division in the form of budding. Multiple division is frequent in 

 Etadiolaria where the endoplasm gives rise to a multiple number of 

 flagellated swarmers which may be of similar or dissimilar size 

 (isospores and anisospores). In some cases both kinds are formed 

 within the same central capsule. Whether these are gametes is a 

 matter which, while probable, has not been satisfactorily proved. 



Among the Heliozoa sexual processes are fully described only 

 for Actinosphaerium and Actinophrys in which the peculiar type of 

 pedogamous isogamy is characteristic (see p. 277). 



The Actinopoda are divided into two fairly well-defined sub-classes 

 — the Heliozoa of Haeckel and the Radiolaria of Joh. Muller. 



Sub-class I. HELIOZOA Haeckel. 



Heliozoa are typically fresh water forms although several species 

 of marine forms are known. They are homaxial and floating in 

 habitat for the most part but stalked and attached forms are occa- 

 sionally met with (Wagnerella borealis, Clathrulina elegans, etc.). 

 They are either naked (Aphrothoraca) or covered by a gelatinous 

 mantle without spicules (Chlamydophora), or with spicules (Chal- 

 arothoraca) or provided with a definite latticed shell (Desmo- 

 thoraca). 



Pseudopodia are typically radial with central axial filaments which 

 penetrate the endoplasm. Here they end, or rather begin, either in 

 a nucleus (Actinophrys, Camptonema nutans, etc.), or in a central 

 kinetic granule called the Centralkorn by Grenadier (1869) (Acan- 

 thocystis, Sphaerastfum, Wagnerella, etc.). In such cases the nucleus 

 is excentric. In Camptonema nutans a single axial filament arises 

 from each of the many nuclei and there are as many pseudopodia 

 as there are nuclei. In Wagnerella borealis the nucleus is in the 

 basal plate, while the central granule, with radiating axial filaments, 

 is in an enlargement at the other end of the stalk. 



The body protoplasm is alveolar and characterized by two zones 

 which in some cases are clearly differentiated as ectoplasm and 

 endoplasm (e.g., Actinosphaerium) but in most genera they are 

 rather indefinite. The ectoplasm is made up of relatively large 

 pseudo-alveoli in Actinophrys and Actinosphaerium and is very dif- 

 ferent from the dense ectoplasm of Ameba. The endoplasm is 

 more finely granular and contains one or more nuclei (up to two 

 hundred or more in Actinosphaerium). Symbiotic forms are not 

 infrequent in the endoplasm and are regarded as aflagellate forms 

 of algae. 



Contractile vacuoles are present in fresh water species but are 

 generally absent in salt water forms. They are developed in the 

 cortex and resemble slightly enlarged ectoplasmic vesicles bursting 

 to the outside. 



