PROTOZOA 



21 



spherical cavities, one or more in number according to the organism; 

 over these in pelliculate genera there is a soft patch in the pellicle 

 through which discharge takes place. Sometimes, as in Eiiglena and 



Fig. 17. 



Fig. 16. 



Fig. 16. Paratnecium caudatiini from the ventral side, x 375. After Doflein. 

 CV, contractile vacuoles: in the anterior one the main vacuole has just dis- 

 appeared by discharging, and is about to be reconstituted from the accessory 

 vacuoles, which are at their maximum size ; in the posterior one the accessory 

 vacuoles having re-formed the main vacuole are themselves re-forming; f.v. 

 food vacuoles ; me. meganucleus ; 7ni. micronucleus ; v. vestibule. 



Fig. 17. The cycle of action of the contractile vacuole and its canals in Para- 

 mecium. From Lloyd, after Putter. 



Paramechifn, they are accompanied by accessory vacuoles by whose 

 contents they are reconstituted (Figs. 39 D, 16, 17) and which in some 

 ciliates (Fig. 89 B, C) extend as long canals through the cytoplasm. 



