80 



ZOOLOGY 



SECT. 



protoplasm : they then contract, discharging the water into the 

 vacuole, the latter rapidly enlarging while they disappear from 



c.vac. 



Fi,;. tin Paraxnoecium caudatum. A, the living animal from the ventral aspect; B, the 

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

 which has discharged its trichocysts ; D, diagram of binary fission ; inn-. </,-. buccal groove ; 

 rih-t. cortex; <-i'. cuticle; c, rue. contractile vacuole;.?'. vdc. fond vacunle ; <n<l. gullet; <!. 

 medulla; nu. meganucleua ; pa. nu. micronucleus ; trek, trichocysts. (From Parker's Biology.) 



view ; finally the vacuole contracts and discharges its contents 

 externally. 



The cortex contains minute radially arranged sack called 

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



