278 PRACTICAL DIRECTIONS CHAP. 



in close relation with the deeper layer on the dorsal side : note that 

 canals radiate from them when they contract ; (e) the cilia lining the 

 buccal groove. (The potential amis behind the mouth can only be 

 seen at the moment of defecation. ) Compare the mode of feeding with 

 that of Amoeba. 



5. The characters of the medulla : (a] The food-vactwles and their 

 circulation ; (b] the meganucleus and micro-nucleus, which can be better 

 seen when stained. Sketch. 



6. Add methyl-green or magenta. Then note again the structure of 

 cortex and medulla, as well as (a) the oval meganucleus, near the 

 middle of the body ; (b] the micronucleus, a smaller body, close to the 

 meganucleus ; (c) the extruded trichocysts. Sketch. 



7. Look out for specimens undergoing transverse fission, and also for 

 others in process of conjugation. Sketch. 



Permanent preparations may be made as directed in the case of 

 Amceba (p. 239). 



Voiticella. 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 anal spot 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- 

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

 there are no trichocysts. Moreover, in the stalk (into which the 

 medulla does not extend) the deeper layer of the cortex gives rise to a 

 central contractile axial fibre, by means of which the stalk can contract 

 spirally. The contractile vacuole is single. 



6. The medulla, which circulates and contains food-vactioles, as in 



