14 BRITISH FRESHWATER HELIOZOA. 



HELIOZOA. 



SARCODINA of spherical form with radiate non- 

 anastomosing pseudopoclia of granular protoplasm; 

 each pseudopod usually having a stiff axial rod 

 passing into the body-plasma ; no central capsule 

 or clear ectoplasm present; skeleton when present 

 non -continuous or perforated, composed of silicious, 

 chitinous, or foreign elements, often bearing radial 

 spines of various shapes ; nucleus in the freshwater 

 genera (except Actinosphaeriuin) single, placed cen- 

 trally or eccentrically ; contractile vacuoles one or 

 more, usually superficial ; reproduction by fission or 

 budding in the active condition or by brood-formation 

 in a cyst giving rise to resting-spores ; conjugation 

 isogamous (so far as known) ; habitat mostly in fresh 

 water, on the bottom of lakes or pools, floating, or 

 attached to weeds. 



