operculum- — 

 motor mass (motorium) 



opercular fibers 



dorsal disk _ _ _ 



dorsa 

 membranelles- 



outer dorsal lip 



outer 

 dorsal furrow 



circumesophageal ring 



oral cilia 

 cytostome 



oral disk 



adoral membranelles 



— -inner adoral lip 

 —outer adoral furrow 

 -outer adoral lip 

 -esophagus or cytopharynx 



esophageal rectrator strands 

 ventral skeletal area 



^skeletal laminae 



ventral side of body 



boundary layer (ectoplasmic) 



ectoplasm- . 



nuclear membrane 

 rectal fibers 



cuticle 



caecum 



rectum 



Frontispiece.— Reconstruction of a sagittal section of a ciliate (Diplodinium 

 ecaudatum) illustrating the extent to which specialization may proceed within the 

 cytoplasm of a single-celled animal. {Redrawn from Sharp.) 



