30 



contractile vacuoles (seen at the periphery). Some (e.g., 

 Acanthocystis) form siliceous skeletons. Green unicellular 

 Algae are often found living in the endoplasm, e.g., a species 

 of Zoochlorella lives in intimate partnership (symbiosis) with 

 certain kinds of Actinosphcerium. Reproduction is asexual 

 by binary fission, or sexual by a process of encystment, 

 involving reduction of nuclei and followed by spore-forma- 

 tion and conjugation of gametes. The Heliozoans are 

 freshwater forms. Actinophrys and Actinosphcerium are 

 common in ditches, ponds, and moor pools. 



Vacuole Nucleus 



Pseudopodium 



Axial Filan 

 Pseudopodium ^ , , ^ ^ ^ ^ 



F IG . 4 Actinophrys, (Magnified.) 



How does Actinosphcerium feed ? 



It preys on active infusorians. When one touches the 

 pseudopodia, these suddenly bend inwards and the creature 

 is trapped. As the bending goes on, swellings appear 

 upon the pseudopodia and these, moving down, push 

 the captive closer in. When it has been brought quite 

 near the body, blunt amoeba-like pseudopodia are pro- 

 truded, and it is then engulfed and passed into the endo- 

 plasm. 



