370 



BIOLOGY OF THE PROTOZOA 



surface but they may encroach on the dorsal surface {c. g., Uron- 

 ychia); they form groups as a rule, named according to their posi- 

 tion, frontal, ventral, anal, and caudal cirri, the number and arrange- 

 ment forming a basis for diagnosis of genera and species. 



•• 





Fig. 161. — Didinium nasutiim capturing and swallowing Paramcciutn caudatum 

 (1 to 6) ; 8, section of Didinium prior to encystment showing protruded seizing organ 

 with zone of trichocysts and rhizoplasts from the membranulse to the nucleus. (After 

 Calkins.) 



