272 VORTICELLA CHAP. 



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 (C) 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 (A, st) consists of a very delicate, trans- 

 parent, 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) : 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 external stimulus. The slightest jar of the micro- 

 scope, the contact of some other organism, or even a 

 current of water produced by some free-swimming form 

 like Paramoecium, is felt directly by the bell-animalcule, 

 and is followed by an instantaneous change in the 

 relative position of its parts. The stalk becomes coiled 

 into a close spiral so as to have a mere fraction of its 

 original length, and the body from being bell-shaped 

 becomes globular, the disc being withdrawn and the 

 peristome closed over it (D 1 , D 2 ). 



