142 BIOLOGY OF THE PROTOZOA 



homologous with the axopodia of motile types and that the latter 

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

 of Dimorpha mutans where two flagella and many axial filaments of 

 axopodia originate from the same blepharoplast (Fig. 12, p. 34). 



Speculations as to ])hylogeny 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 AdinosplKBrium 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 Clathrvlina 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 ele- 

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

 stereoplasm (Fig. 73, C). 



Rhizopodia.— This type of pseudopodia differs from others, first, 

 in the tendenc}^ to branch, and second in the tendency to fuse or 

 anastomose when such branches meet. From these characteristics 

 they are sometimes called reticulose pseudopodia and myxopodia. 

 So far as number of species is concerned, this type is the most 

 characteristic form of Sarcodina pseudopodia. They occur in all 

 forms of Foraminifera, Radiolaria and Mycetozoa which include 

 the great majority of Protozoa. As a result of their unlimited power 

 to branch arid to anastomose, great meshworks of reticulated proto- 

 plasm are created which make ideal traps for the capture of food. 

 In man\' types, especially in Radiolaria, they birx be long and ray- 

 like, with relatively little tendency to fuse; in other cases a main 

 trunk gives rise to so many branches that it is lost in the reticulum, 

 great accumidations of protoplasm collecting at the branching points 



(Fig. 9,P--1)- 



Doflein includes axopodia and these l)ranching anastomosing 

 pseudopodia in the one type rhizopodia, and sees in the axial fila- 

 ment of the former and the inner protoplasm of the latter, only 

 different states of the same fundamental stereoplasm. Axial fila- 

 ments, however, derived from the substance of kinetic centers, are 

 quite different from structureless axial stereoplasm which has no 

 relation to kinetic elements. The enveloping protoplasm is appar- 

 ently the same in both types and granule streaming is a common 

 property, but the physical consistency is quite different. In rhizo- 

 podia the outer protoplasm is soft and miscible, leading to fusion on 

 contact with one another, while axopodia never anastomose. The 

 denser core of rhizopodia, while not condensed to a single fiber, 

 serves the same function of support as the axial filament of Actino- 

 sphcerium and gives stiffness and rigidity to long ray-like pseudo- 



