THE SARCODINA 



79 



B. PSEUDOPODIA 



A pseudopodium is a portion of the body-plasm temporarily pro- 

 truded. It is most variable in form, and at any moment can be with- 

 drawn into the body of the animal to be replaced by others. In the 

 Rhizopoda, the pseudopodia are coarse, blunt, and finger-formed 

 (Amcebida), or fine, and often 

 forming a network through 

 anastomosis (Reticulariida). 

 In the Heliozoa and Radio- 

 laria they are more rigid and 

 radiate out from the body in 

 all directions, forming a pro- 

 tective coating, and from their 

 ray-like appearance suggest- 

 ing the common name " sun- 

 animalcula." 



There is a difference in the 

 texture as well as in the form 

 of the lobose and reticulate 

 pseudopodia of the Rhizop- 

 oda. In the former the hya- 

 line ectoplasm, which goes 

 into the pseudopodia, is ap- 

 parently homogeneous and 

 structureless, although, upon 

 critical examination, Biitschli 

 {'92) was able to make out a fibrous structure in some forms, and 

 in many of them a reticular appearance was obtained upon retrac- 

 tion. His observations led him to the conclusion that the hyaline 

 appearance is due to the close approximation of the walls of the 

 alveoli, and not to their absence. The outer plasm is certainly more 

 dense and non-granular than the endoplasm, and protoplasmic stream- 

 ing is confined to the latter. The outer plasm in the reticulate type, 

 on the other hand, is granular, while the central portion is denser and 

 more resisting. Streaming of the granules here takes place in the 

 ectoplasm, instead of in the endoplasm, and when two or more pseu- 

 dopodia come in contact, the viscid character of this outer plasm leads 

 to fusion. The lobose forms, on the other hand, never coalesce. 



The resemblance between the central denser strand of protoplasm 

 in the pseudopodia of the reticulate type and the axial filament of the 

 pseudopodia of Heliozoa and Radiolaria was early recognized bv M. 

 Schultze('63) and critically examined by Biitschli ('92) and Schaudinn 

 ( '93), and is now generally recognized. 



Fig. 43. — Plagiocarpa. frocortuia Haeck., 

 tripod-like skeleton. [HAECKEL.J 



