ii PHYLUM >ROTOZOA 89 



protoplasm: they then contract, discharging the water into the 

 vacuole, the latter rapidly enlarging while they disappear from 



c.rac 



nrt. 



FIG. 69. 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 ; G, a specimen 

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

 cort. cortex; en. cuticle; c. roc. contractile vacuole;/. roc. food vacuole; gul. gullet; rued. 

 medulla; /nMnegnimcleus ; pa. nu. imeronncleus ; 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 



