II 



PHYLUM PROTOZOA 



89 



protoplasm : they then contract, discharging the water into the 

 vacuole, the latter rapidly enlarging while they disappear from 



B 



rac 



C.TUC 



me. 



FIG. 69. Paramoecium caudatum. A, the living animal from the ventral aspect ; B, the 

 same in optical section : the arrow shows the covirse taken by food-particles ; C, a specimen 

 which has discharged its trichocysts ; D, diagram of binary fission ; buc. (jr. buccal groove ; 

 corf, cortex ; cu. cuticle ; c. vac. contractile vacuole ; /. vac. food vacuole j (iul. gullet ; med. 

 medulla; nu. meganucleus ; pa. mi. micronucleus ; trch. trichocysts. (From Parker's Biology. ) 



view ; finally the vacuole contracts and discharges its contents 

 externally. 



The cortex contains minute radially arranged sacs called 

 trichocysts (trch.). When the animal is irritated, more or fewer of 



