in PRACTICAL DIRECTIONS 287 



from them when they contract ; («) the cilia lining the buccal groove. 

 (The potential anus behind the mouth can only be seen at the moment 

 of defjecation. ) Compare the mode of feeding with that of Amoeba. 



5. The characters of the medulla : — (a) The food vacuoles and their 

 circulation ; {b) the meganucteus and micronucleus, which can be better 

 seen when stained. Sketch. 



6. Add methyl green. Then note again the structure of cortex and 

 medulla, as well as — (a) the oval megamuleus, near the middle of the 

 body ; (iJ) the micronucleus, a smaller body, close to the meganucleus ; 

 (c) the extruded trichocysts. Sketch. 



7. Look out for specimens undergoing transverse _/fi'«'o«, and also for 

 others in process of conjugation. Sketch. 



Permanent preparations may be made as directed in the case of 

 Amoeba (p. 239). 



Opalina. — Make an incision in the rectum or small intestine 

 of a freshly-killed frog, and mount a little of its contents in water on 

 a slide. Note the oval and flattened form of the OpalinEe and their 

 uniform covering of cilia ; the cuticle, cortex and viedulla ; and the 

 absence of a mouth and contractile vacuole. Stain as before, and 

 make out the numerous nticlei. Look out for the products of division 

 free and encysted. 



Vorticella. Mount some specimens in a drop of water, and examine 

 with the low power. The Vorticella will be seen to have the form 

 of a wine-glass or bell with a long stem. The stem frequently contracts 

 spirally, the edge of the bell being at the same time turned in, so as to 

 give the animal a rounded form. Put on the high power and note — 



1. The form of the bell, its thickened rim or peristome, and the disc, 

 which forms a cover to the bell. 



2. The mouth and gullet, opening on one side between the peristome 

 and disc, which is here slightly raised. (The anus opens :into the oral 

 depression, but can only be seen at the moment of defsecation.) 



3. The single row of cilia round' the peristome and extending down 

 the gullet on the one hand, and on to the raised portion of the disc on 

 the other. Run in a little finely powdered indigo or carmine under the 

 cover-glass, and note the currents produced by the cilia : the granules 

 of pigment will be carried down the gullet. 



4. The contractions of the bell and stalk. 



5. The structure of the cortex, which is similar to that of Para- 

 moecium, except that the cilia have a restricted distribution, and that 



