STRUCTURE OF STYLON\'CHIA 



117 



In correspondence with this, instead of being nearly 

 cylindrical, it is flattened on one — the ventral — side, 

 and is thus irregularly plano-convex in transverse section 

 (Fig. 22, c). 



--nuci 



Fig. 22. — A, Slylonychiii iiiylilus, ventral aspect, showing the buccal 

 groove {buc. gr.) and mouth (tnth), two nuclei («//, nii), coiilractile 

 vacuole {c. vac), and cilia differentiated into hook-like (h. ci). tristle- 

 like (b. ci), plate-like (/. «), and fan-like (in. ci) organs. 



B, one of the plate-like cilia of the same (/. ci in A), showing its 

 •frayed extremity. 



c, transverse section of Castrostyla, a form allied to Stylonychia, 

 showing buccal groove (liuc. gr.), small dorsal cilia (</. ci), hook-like 

 cilium \h. ci), and the various cilia of the buccal groove, including an 

 expanded fan-like organ (m. ci). A and B after Claparede and Lach- 

 mann : c after Sterki. 



It resembles Paramoecium in general structure (compare 

 Fig. 22, A, with Fig. 20, a); but owing to the absence of 

 trichocysts the distinction between cortex and medulla is 



