B 



c.vac 



c.vac. 



/T"A /// 



:/\ : 



.;# 1- 



pa.nu 



FIG. 18. Paramcecium caudatum. A, the living animal from the ventral aspect; 



B, the same in optical section : the arrow shows the course taloen by food-particles ; 



C, a specimen which has discharged its trichocysts; D, diagram of binary fission; 

 buc. .g-r, buccal groove; corf, cortex; cu, cuticle; c. vac, contractile vacuole; _/". 

 vac food vacuole; gul, gullet; wed, medulla; , meganucleus; fa. nu, micro- 

 nucleus; trch, trichocysts. (From Parker's Biology.') 



47 



