368 Ciliophora 



Fig. 7. 21. A. Reproductive cyst of Ichthyophthirius multifiliis Fouquet, 

 cross-section, nuclei indicated but cilia not shown; x450 (after MacLennan). 

 B. Ciliated larva of /. multifiliis just after excystnient; "perforatoriinn" at 

 anterior end, cytostome not differentiated; x750 (after MacLennan). C. 

 Longitudinal section through oral region of matme specimen of /. multifiliis, 

 embedded in epithelium of fish; x370 (after MacLennan). D, E. Ophryoglena 

 atra Lieberkiikn: ventral view (D) of specimen 400/i long; schematic repre- 

 sentation (E) of vestibular ciliatuie and body of Lieberkiihn (after Rahl). 

 F. Ptychostomum (Lada) pygostoma (Rossolimo); length reaches 200^; un- 

 dulating membrane extends through posterior cytostome into pharynx 

 (after R.). G-L Hysterocineta eiseniae Beers (after B.): ventral view of 

 posterior end (G), showing undulating membrane extending along the 

 peristomial groove and into the pharynx, x600; dorsal view (H), the ventral 

 sucker shown in outline at the anterior end, x285; lateral view (I), x285. 



production. In Ichthyophthirius (145), fission produces many (100-1,000) 

 small ciliates which are set free with an incompletely developed mouth. 

 These active stages (Fig. 7. 21, B) swim about until they either starve to 

 death or encounter a suitable fish. In the latter case, the ciliate apparently 

 bores its way into the tissue as a result of strong ciliary action. After pene- 



