STALK AND AXIAL FIBRE 127 



The : movements of the cilia produce a very curious 

 optical illusion : as one watches a fully-expanded specimen 

 it is hardly possible to believe that the peristome and disc 

 are not actually revolving a state of things which would 

 imply that they were discontinuous from the rest of the 

 body. As a matter of fact the appearance is due to the 

 successive contraction of all the cilia in the same direction, 

 and is analogous to that produced by a strong wind on a 

 field of corn or long grass. The bending down of suc- 

 cessive blades of grass produces the appearance of waves 

 travelling across the field in the direction of the wind. If 

 instead of a field we had a large circle of grass, and if this 

 were acted upon by a cyclone, the wave would travel round 

 the circle, which would then appear to revolve. 



Naturally the movement of the circlet of cilia produces a 

 small whirlpool in the neighbourhood of the Vorticella, as 

 can be seen by introducing finely-powdered carmine into 

 the water. It is in this way that food particles are taken 

 in, surrounded as in Paramcecium by a globule of water : 

 the food-vacuoles (f. vac] thus constituted circulate in the 

 medullary protoplasm, and the non-nutritive parts are finally 

 egested at an anal spot (an) situated near the base of the 

 gullet. 



The stalk (sf) consists of a very delicate, transparent, 

 outer substance, which is continuous with the cuticle of the 

 body and contains a delicate axial fibre (ax. f) running 

 along it from end to end in a somewhat spiral direction. 

 This fibre is a prolongation of the cortex of the body 

 (c, ax. f.) : under a very high power it appears granular or 

 delicately striated, the striae being continued into the cortex 

 of the proximal part of the body. 



A striking characteristic of Vorticella is its extreme 

 irritability, i.e., the readiness with which it responds to any 



