14 



ESSENTIALS OF ZOOLOGY 



myonemes are produced at the base of the bell to form a 

 spirally directed contractile filament which ends in the ad- 

 hesive disc of the peduncle. The peduncle thus consists of 



Disc 



Micronucleus 

 Macronucleus 



Contractile filament 

 of stalk 



Collar 



Vestibule 

 Contractile vacuole 



Food vacuole 



FIG. 6. Diagrams of Vorticella in the expanded and contracted state. 



a cortical layer and a central filament. Vorticella responds 

 readily to movements conveyed through the water. The disc 

 is withdrawn and covered by the contracted collar, and the 

 peduncle is shortened by being thrown into a spiral. It is 



