in VORTICELLA 269 



It will be noticed that, in the present instance, conjugation 

 is not a process of multiplication : it has been ascertained 

 that during the time two infusors are conjugating each 

 might have produced a very large number of offspring by 

 continuing to undergo fission at the usual rate. The im- 

 portance of the process lies in the exchange of nuclear 

 material between the two conjugating individuals. 



The next organism we have to consider is a ciliate infusor 

 even commoner than that just described. It is hardly 

 possible to examine the water of a pond with any care with- 

 out finding in it, sometimes attached to weeds, some- 

 times to the legs of water-fleas, sometimes to the sticks and 

 stones of the bottom, numbers of exquisitely beautiful little 

 creatures, each like an inverted bell with a very long handle, 

 or a wine-glass with a very long stem. These are the 

 well-known " bell-animalcules," the commonest among them 

 belonging to various species of the genus Vorticella. 



The first thing that strikes one about Vorticella (Fig. 72, A) 

 is the fact that it is permanently fixed, like a plant, the 

 proximal or near end of the stalk being always firmly fixed 

 to some aquatic object, while to the distal or far end the 

 body proper of the animalcule is attached. 



But in spite of its peculiar form it presents certain very 

 obvious points of resemblance to Paramcecium. The 

 protoplasm is divided into cortex (c, corf] and medulla 

 (med\ and is invested with a delicate cuticle (cu). There is 

 a single contractile vacuole (c. vac) the movements of which 

 are very readily made out owing to the ease with which the 

 attached organism is kept under observation. There is a 

 meganucleus (nu) remarkable for its elongated band-like 

 form, and having in its neighbourhood a minute micro- 

 nucleus. Cilia are also present, but the way in which 



