Chap. III.] 



GROUPS OF PROTOZOA. 



29 



The Heliozoa either have the body naked or a 

 siliceous skeleton is developed ; the body is very com- 

 monly spherical in shape, while the pseudopodia 

 (Fig. 2 B) are fine, alter but little in form, and rarely 

 anastomose with one another ; lastly, the Radiolaria 

 (Fig. 2 c) have a chitinous " central capsule," around 

 which flows the protoplasm, and with which there is 



Fig. 3 I. Paramcecium aurelia ; A, from the side ; B, from below ; c, two in 



conjugation, 

 n, Nucleus ; b, mouth ; cv, contractile vacuole. 



ordinarily connected a delicate and often elaborate 

 siliceous skeleton. The pseudopodia are less constant 

 in form than in the Heliozoa, and enter into anasto- 

 moses with their neighbours. 



The Infusoria are ordinarily ciliated, but in 

 some (Flagellata) the cilia are replaced by a single 

 long whip-like process of protoplasm (flagellum) 

 (Fig. 3 ii.), and in others which are parasitic on 

 (ectoparasitic) the bodies of other infusorians, the 

 cilia are lost and replaced by tentacle-like sucking 

 tubes (Fig. 3 in.). 



