PHYLUM PROTOZOA 



57 



One genus has a shell formed of agglutinated sand-grains ; in 

 another (Fig. 39, A) the skeleton consists of loosely matted needles 



3.Cla>hru.lina 



FIG. 39. Various forms of Helicrzoa. 8a, the entire animal; Sb, the flagellula ; c. vac. 

 contractile vacuole ; g. gelatinous investment ; nu. nucleus psd. pseudopods ; sk. siliceous 

 skeleton ; sp. spicules. (From Butschli's Protozoa, after Schulze and Greeff.) 



of silica. Lastly, in the graceful Clathrulina (3) the body is 

 enclosed in a perforated sphere of silica, quite like the skeleton of 

 many of the Radiolaria (vide infrci). 



