I. RHIZOPODA: HELIOZOA. 



191 



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

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



\ 



FIG. 121. Clathrulina elegam. A, with extended pseudoppdia; JB, divided into two 

 cysts ; C, zoospore ; n, nucleus ; cv, 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, C). 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 proto- 

 plasmic bridges, and so form unions of 

 from two to ten individuals. True fer- 

 tilization preceded by a kind of polar- Flo . 122 .-cyst with germinal 

 globule formation has only been ob- 

 served in Actinoplirys sol and Act ino splicer ium eiclihorni. 



