CHAPTER XII 

 THE CILIATA (continued) VORTICELLA 



THE genus which we are now going to study is very common 

 and rich in species. Specimens may be collected during the 

 warmer months in almost any freshwater pool or ditch, where 

 they are generally found adhering to the stalks of water-weeds. 

 Or one may nearly certainly obtain a cultivation of Vorticella 

 by making an infusion of hay and dead leaves in soft water 

 and leaving it to stand for a time. After the first stages of 

 putrescence have passed a thick brown scum will form on the 

 surface, and numerous specimens of Vorticella will be found 

 adhering to the under side of this scum. 



There are many species of Vorticella, differing from one 

 another in so small a degree that it is often very difficult to 

 identify them. The following description refers chiefly to 

 Vorticella monilata, a species which frequently makes its ap- 

 pearance in vegetable infusions, and is easily recognisable 

 because of the warty excrescences with which its body is 

 studded. 



In shape Vorticella may be compared to an inverted bell, 

 with a very long handle. Imagine the rim of the bell to be 

 thickened and beset with a circle of cilia, and its mouth to be 

 almost closed by a discoidal plug, placed to one side so as to 

 leave between it and the thickened rim a slit leading into the 

 interior. Further, imagine that the handle is hollow and 

 traversed by a contractile cord thrown into a loose spiral so 

 that on contraction of the cord it is shortened into a close 

 corkscrew-like spiral, and one has a very fair idea of the 

 general appearance of the organism. 



In the genus Vorticella the individuals may be closely 

 crowded together or may stand at some little distance apart on 

 the weed or other substance to which the stems are attached, 

 but they are always separate and independent of one another. 

 In the closely allied genera Zoothamnium and Carchesium the 



234 



