VORTICELLA 



is termed the meganucleus; beside it lies a very much smaller 

 one termed the micronucleus (Fig. 12). When a Vorticella is 

 irritated, the peristomial lip is turned in so as to lie against the disc, 

 and thus the groove in which the cilia lie becomes converted into a 

 tube and so they are efficiently protected. 



Fm. 12. 



Diagram of Vorticella. The cilia at the side of the mouth have 

 been omitted. 



1. Disc. 2. Mouth. 3. Peristomial groove. 4. Vibratile membrane in 

 mouth. 5. Cortical layer. 6. Endoplasm. 7. Food-vacuoles. The 

 last of the food-vacuoles is nearing the position of the anus. 8. Pharynx 

 showing formation of food-vacuoles. 9. Contractile vacuole. 10. Per- 

 manent receptacle into which the contractile vacuole opens. 11. Micro- 

 nucleus. 12. Meganucleus. 13. Contractile fibrils running into 

 muscle in stalk. 14. Stalk contracted (the axial fibre should touch the 

 cuticle in places). 



We have seen above that Vwrticella uses its cilia in order to 

 produce a miniature whirlpool in the water by means of which 

 particles of edible matter whether living or not are drawn 

 towards it. Since, however, it possesses a firm cuticle and in 

 addition a specialised outer layer of protoplasm, the question arises 

 how the food is taken into the interior of the body. If we run 



