xii AXIAL FIBRE 129 



disc ; the whole row of cilia thus takes a spiral direction. 

 The rest of the body is completely bare of cilia. 



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 a series 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 through the agency of this whirlpool that 

 food particles are swept into the mouth, surrounded, as in 

 Paramcecium, by a globule of water : the food-vacuoles 

 (/ vac) thus constituted circulate in the medullary proto- 

 plasm, and the non-nutritive parts are finally egested at an 

 anal spot (an) situated near the base of the gullet. 



The stalk (st) 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. 



