DERIVED ORGANIZATION— TAXONOMIC STRUCTURES 147 



endoplasmic kinetic elements. Gymnosphaera, Raphidiophrys, 

 Sphaerastrum, Acanthocystis, Dimorpha, etc., possess characteristic 

 "central grannies" which, from their activities in cell division, are 

 unmistakably centroblepharoplasts (see p. 117) from the substance 

 of which the axial filaments are formed (Fig. 50, p. 95). Wagner- 

 ella borealis, in addition to the central granule, possesses a zone of 

 basal bodies which give rise to the axial filaments and which at 

 times of retraction of the pseudopodia are drawn into the central 

 granule. In still other cases, as in Actinosphaerium eichhornii, the 

 axial filaments do not arise, apparently, either from central granules 

 or from nuclei, but appear to start indefinitely in the cytoplasmic 

 reticulum (Fig. 78, D). 



While the more common forms of Heliozoa are quiescent, floating 

 types, some of the Heliozoa are freely motile. Acanthocystis acu- 

 leata, as well as other species of the same genus, turns slowly over 

 and over in a rolling movement; Camptonema nutans, according to 

 Schaudinn, bends and straightens its axopodia in food-getting and 

 in other activities. Actinosphaerium eichhornii and Actinophrys sol 

 are practically motionless. The active movements are due to the 

 axopodia and the structure of axopodia is strikingly like that of 

 flagella. That the contractile axial filament is the seat of this 

 movement, and not the enveloping protoplasm, is not open to 

 reasonable doubt. Structure, function and mode of origin thus 

 justify the inclusion of axopodia with the kinetic elements of the 

 cell. 



On the other hand, in type-, with axopodia which are practically 

 motionless, the axial filaments have apparently lost the vibratile 

 function and now serve as supporting elements for the long radiating 

 pseudopodia. There is little reason to doubt that such elements are 

 homologous with the axopodia of motile types and that the latter 

 are homologous with flagella. This is well illustrated by the case 

 of Dimorpha mutatis where two flagella and many axial filaments 

 of axopodia originate from the same blepharoplast (Fig. 79.) 



Speculations as to phylogeny on purely morphological grounds 

 are not profitable, but in this group of Heliozoa we have pretty good 

 evidence of a close relationship between flagellates and Sarcodina, 

 and equally good evidence of the transition from an active kinetic- 

 element to an inactive, supporting axial rod, as seen in the pseudo- 

 podia of Actinosphaerium eichhornii. This change in type is prob- 

 ably associated with the loss of specific kinetic centers for neither in 

 the cytoplasm nor in the nuclei are such elements to be found. In 

 some forms, finally, notably in Clathrulina elegans, the ends of the 

 axopodia are frequently branched, a condition which points the 

 way to pseudopodia of the rhizopodia type in which the supporting 

 element is not in the form of an axial rod, but in the form of stiff 

 stereoplasm (Fig. 78, C). The pseudopodia of Clathrulina, which 



