/. RHIZOPOBA: HELIOZOA. 



191 



Heliozoa possess a silicious skeleton, -which may be a lattice-work 

 sphere (fig. 121), needles radially arranged or placed tangen- 



Fio. 121- — ClathruUna eJegans. A, with extended pseudopodia; B, divided into two 

 cysts: G, zoospore; n, nucleus; cu, contractile vacuole. 



tially. The forms without skeletons are few, but these have the 

 power (fig. 122) of forming silicious envelopes during encystment. 



Reproduction takes place by divi- 

 sion, and one or both moieties may 

 become swarm spores, i.e., assume an 

 oval form bearing at one pole one or two 

 flagella (fig. 121, 0). These swarm 

 spores become widely distributed by 

 the flagella before they resume the 

 spherical shape, lose their flagella and 

 form pseudopodia. It frequently occurs 

 that several Heliozoa of the same 

 .species become connected by jjroto- 

 plasmic bridges, and so form unions of 

 from two to ten individuals. True fer- 

 tilization preceded by a kind of polar- fio 

 gloljule formation has only been ob- 

 served in Actinophrys sol and AcHuosphcBriu»i eichltoriii 



122. — Cyst with germma. 

 spheres of Ai'ti}iosjj}iin'hiii-i eich- 

 hiirni. (After F. E. Schulze.) 



