per 



FIG. 25. Vorticella . 



A, living specimen fully expanded, showing stalk (st) with axial fibre 

 (ax. f), peristome (per), disc (d), mouth (nith), gullet (gnll), and 

 contractile vacuole (c. vac). 



B, the same, bent on its stalk and with the disc turned away from the 

 observer. 



C, optical section of the same, showing cuticle (cti), cortex (cort), 

 medulla (med), nucleus (), gullet (gull), several food-vacuoles, and 

 anus (an), as well as the structures shown in A. 



D l , a half- retracted and D* a fully-retracted specimen, showing the 

 coiling of the stalk and overlapping of the disc by the peristome. 



