THE SARCODINA 105 



other flagellated forms, perhaps from forms like the Vampyrellidse. 

 On the whole, there is no conclusive evidence to support the view that 

 Rhizopoda are more primitive than Flagellidia, or vice versa. Their 

 mutual affinities are very close, and together they stand as the most 

 primitive forms of modern Protozoa. 



The relations of the Radiolaria to the Heliozoa are extremely close, 

 and there is abundant evidence to show that the former were derived 

 from the latter by the acquisition of a chitinous membrane between 

 ectoplasm and endoplasm, and the retention of a gelatinous mantle 

 like that of Sphczrastrum (Haeckel). As first pointed out by Brandt 

 ('85), the young Radiolaria pass through flagellated and amoeboid 

 swarm stages, then through Heliozoa stages, until the definitive 

 radiolarian structure is attained. Haeckel described the intermediate 

 forms which are represented in this growth, as flagellate, amoeboid, 

 Actinophrys, Sphczrastrum, and Actissa, the last being the simplest of 

 the Radiolaria. Although the external appearance of a radiolarian 

 is strikingly similar to that of a heliozoon, there is no structure in 

 Heliozoa to compare with the chitinous central capsule of the Radio- 

 laria. Greeff ('67, '71) described a membrane-like thickening between 

 the endoplasm and the ectoplasm of Actinospharium, and regarded it 

 as homologous with the central capsule. Other observers, e.g. F. E. 

 Schultze, Hertwig and Lesser, Biitschli, etc., have not seen it, and 

 the latter, especially, considers Greeff's contribution of little value. 

 However incorrect his interpretation may have been that Actinosplice- 

 riitm is a fresh-water radiolarian belonging to the Acantharia, Greeff 

 was not mistaken in his observation, for an occasional specimen is 

 found which shows such a membrane (Fig. 58). 



CLASSIFICATION 



Class I. SARCODINA. Naked or shelled Protozoa, characterized by the possession 

 during adult life of movable or changeable processes of protoplasm, the pseudo- 

 podia, which may be finger-form, reticulate, or ray-like, and which may or may 

 not have axial filaments. Reproduction is brought about by simple division and 

 by spore-formation. 



Subclass I. RHIZOPODA. Naked or shelled Sarcodina having pseudopodia of the 

 lobose (finger-formed) or reticulate (anastomosing) type. The adult form is 

 amoeboid : the young forms are amoeboid or flagellated, and are produced by 

 spontaneous division of the cell during active phases or during encystment. 

 The adults in some cases fuse to form plasmodia. 



Order 1 . AMCEBIDA. Rhizopoda provided with lobose pseudopodia, with or with- 

 out a shell, with one or more nuclei, and usually with a contractile vacuole. 



Suborder 1. GYMKAMCEBINA. Naked forms of Amcebida having lobose pseudo- 

 podia, and with or without nucleus and contractile vacuoles. 



Family 1. AMCEBIDiE. The pseudopodia are lobose, occasionally sharp pointed 

 and branched. Genera: Amceba, marine and fresh water; Paramceba Schau- 

 dinn ('96); Protamasba Haeckel ('66), marine and fresh water; Cringa 



