I , 



THE S ARC ODIN A 



dence to show that pseudopodia and flagella are closely related, and 

 this evidence is strong enough, I believe, to throw additional light 

 upon the Flagellidia, regarded as the most primitive forms of Proto- 

 zoa. It has been shown that the flagellum in most cases arises in the 

 vicinity of the nucleus. This is also the case with the axial filaments 

 of the Heliozoa, an extremely interesting example being shown in the 

 form Dimorpha, as described by Gruber (Fig. 55, also Fig 46, p. 82). 

 Here the axial filament is homologous with the flagellum, and there 

 is ground for believing that the homology can be carried from 

 Dimorpha to the true Heliozoa, where all of the appendages are simi- 

 lar to the axopodia of Dimorpha. Thus, in Acanthocystis and Actino- 

 phrys, the axial filaments radiate from a common centre in the 

 nucleus (Actinophrys, see Fig. 54 A\ or in the cytoplasm (Acantho- 

 cystis). In Actinosphcerium and Camptonema, they arise from the 

 nuclei and do not converge at a common point. In these particular 

 cases, the pseudopodia have little power of vibratile motion, such as 

 we might expect if the axial filaments are comparable with flagella. 

 In other cases they do possess this power, however, to a certain 

 degree, as shown by the rolling motion of Acanthocystis, which is able 

 to travel a distance equal to twelve times its own diameter in one 

 minute, or by the quick dancing motion of Artodiscus (Penard). 

 That this motion is due to the vibrations or elasticity of the axial 

 filaments I think there can be no doubt, and these structures are 

 comparable therefore with the flagella of the Mastigophora. Unlike 

 flagella, however, they are covered by plastic and streaming proto- 

 plasm, which gives them their pseudopodial character. In those 

 forms of Heliozoa which are usually regarded as more primitive, 

 e.g. Nuclearia and Vampyrella, the axial filaments are not formed, 

 and it is an important question whether these are primitive forms 

 representing a condition before differentiation of the axial filaments 

 in other Heliozoa, or are to be considered as degenerate forms in 

 which the axial filaments have disappeared (Fig. 56). If this question 

 could be answered, it might afford evidence as to whether the Flagel- 

 lidia or the Sarcodina are the more primitive forms ; for if degener- 

 ate, they point toward the Heliozoa or Radiolaria as the ancestors of 

 the reticulate Rhizopoda ; but if primitive, they point toward the 

 Rhizopoda as the ancestors of Heliozoa and Radiolaria, and, through 

 Dimorpha, of the Flagellidia. Evidences of the axial filaments are 

 found in other Sarcodina than the Heliozoa and Radiolaria. In the 

 Reticulariida the central plasm of the pseudopodia is denser and more 

 resisting than the outer plasm, and M. Schultze, Biitschli, Schaudinn, 

 Rhumbler, and others, assume that it has a contractile function ; mor- 

 phologically and physiologically, therefore, it appears to be similar to 

 the axial filaments of Heliozoa, and to the flagella of Mastigophora. 



