PHYLUM PROTOZOA 



89 



protoplasm: they then contract, discharging the water into the 

 vacuole, the latter rapidly enlarging while they disappear from 



c.rac. 



Ttuc. 97: 



Fn;.»'"— Paramoecium caudatum A, the living animal from the ventral aspect; B, the 



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



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



cortex ; c». cuticle ; c. vac. contractile vacuole ; /. vac. food vacuole ; irul. gullet ; med. 



medulla; Hi'.meganucleus; 3x1. nu. 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 



