90 PHYLUM PROTOZOA THE SIMPLEST ANIMALS. 



along with drops of water, which form food vacuoles in the 

 cell substance. Into these vacuoles digestive ferments flow. 

 After the digestible parts of the food have been absorbed, 

 the undigested residue is got rid of at any point of the 

 protoplasm. One or more contractile vacuoles are visible 

 in the cell substance. They have an excretory function, 

 and serve to get rid of the finer waste products. 



Life history. In favourable nutritive conditions the 

 Amceba grows. At the limit of growth it reproduces by 

 dividing into two. In disadvantageous conditions, such as 

 drought, it may become globular, and, secreting a cell wall 

 or cyst, lie dormant for a time. The cyst wall is said to be 

 chitinoid. With the return of favourable conditions the 



FlG. 35. Life history of Amceba. 



i. Amoeba with pseudopodia; ., nucleus; c.v., contractile vacuole. 2. Division 

 in two. 3. Encystation. 4. Escape of Amoeba from its cyst. 



Amoeba revives, and, bursting from the cyst with renewed 

 energy, recommences the cell-cycle. The conjugation of 

 two Amoebae has been observed, and spore - formation 

 occasionally occurs. 



Second Type of Protozoa ACTINOPHRYS 



The Sun-animalcule, Actinophrys so!, is a type of the 

 Heliozoa. 



Description. Like most other Heliozoa, Actinophrys 

 lives in fresh water, floating about or rolling over the 

 bottom. It is spherical and minute, measuring at most 

 0*05 mm. in diameter. Long stiff pseudopodia radiate 

 out from the body. A clear axial filament runs up each 

 pseudopodium, and the small organisms on which Actino- 



