148 



BIOLOGY OF THE PROTOZOA 



have no axial filaments, appear to be transitional to those of the 

 testate rhizopods to which group Valkanov (1928) assigns them. 

 In this stalked form (Fig. 82), however, the stalk takes its origin 

 from the nucleus, as Valkanov clearly shows, and at some stages, at 

 least, has a fibrillar structure. This suggests the possibility that 

 the stalk of Clathrulina (and of Hedriocystis) may represent the con- 

 crescence of ancestral axial filaments. 



B 



Fig. 79. — Dimorpha mutans. Vegetative individual with two flagella and axopodia. 

 Axial filaments of axopodia and flagella meet in a common central granule. At 

 division the central granule divides and forms the poles of the mitotic figure, while 

 the axial filaments form astral rays. X 1950. (After Belaf, Allgemeine Biologie, 

 1927; B. Ergeb. u. Fortschritte d. Zoologie, courtesy of G. Fischer.) 



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

 in the tendency 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 and to anastomose, great meshworks of reticulated proto- 

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



