ORGANS OF LOCOMOTION OF PROTOZOA 



37 



siderable interest from a theoretical point of view, and indicate a 

 possible line of evolution which the protozoa may have followed in the 

 past (Fig. 14). 



The Heliozoa possessing these axiopodia are not very numerous 

 nor are there many species; they are never parasitic and are mainly 

 confined to fresh water, only a few being found in the sea. Another 

 group, however, closely allied to the Heliozoa, the Radiolaria, are 

 exclusively marine. More than four thousand species of these marine 

 forms are known, and they are provided for the most part with the same 

 kind of pseudopodia as those of the Heliozoa, while the great majority 

 of them possess supporting skeletons of acanthin or silica, often 

 exquisitely designed (Fig. 1.3). 



Fig. 14 



Myriophrys paradoxa, P^nard. (From Lang after Pfenard.) 

 axiopodia and fiageiliform cilia. 



Heliozoon with 



Still another type of pseudopodia which may be considered inter- 

 mediate between the lobose and the filose types is the reticulose type, 

 so called from the side streams of protoplasm which start from the 

 central streams and fuse or anastomose with other pseudopodia form- 

 ing a network or reticulum of protoplasm. The calcareous shells of 

 these forms are usually perforated, so that their pseudopodia have 

 easy access to the surrounding medium. Such perforations gave rise 

 to the term foramen- or window-bearing, and under the name Fora- 

 minifera these rhizopods have been known ever since D'Orbigny gave 

 the name in 1823. In addition to the function of locomotion, the 

 pseudopodia of these forms become a trap for diatoms, other protozoa 

 or larval stages of higher forms, the sticky protoplasm making escape 

 very difficult, while the struggles of the prey stimulate an additional 

 flow of protoplasmic secretions by which digestion takes place. 



