m 



VORTICELLA 269 



independent existence, when ordinary transverse fission 

 again takes place. 



It will be noticed that, in the present instance (see 

 also p. 251), conjugation is not a process of multiplica- 

 tion : 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 importance 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 without finding in it, sometimes attached to 

 weeds, sometimes 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 belong- 

 ing 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, cort) and 

 medulla (med], and is invested with a delicate cuticle (cu). 

 There is a single contractile vacuole (c. vac) the move- 

 ments of which are very readily made out owing to the 

 ease with which the attached organism is kept under 



