THE PROTOZOA 



IV. VOETICELLA. 



Vortieella, which is just recognisable with the naked eye, 

 differs from the two preceding infusorians in being attached 

 by a contractile stalk to plants or other objects, often to other 

 aquatic animals ; it may, however, under certain conditions 

 become detached from its stalk and swim freely. 



Both freshwater and marine forms of Vortieella are knbwn. 

 The following description applies more particularly to some 

 of the larger freshwater species, but most of the marine forms 

 closely resemble these. 



Mount a specimen in a drop of water together ■ with a hit 

 of the weed or other substance to which it is attached. 

 Examine it microscopically. 



A. General appearance. 



1. The form of the fully expanded animal is bell-shaped, the 



mouth of the bell being closed by the circular disc, 

 and the handle of the bell represented by the slender 

 stalk by which the animal is attached. The disc is 

 placed somewhat obliquely : it is in contact with 

 the edge of the bell at the ' dorsal ' surface, but 

 separated from it in most forms by a groove at the 

 opposite or ' ventral ' edge. 



2. The peristome is the thickened everted margin of the 



bell. 



3. A fringe of cilia runs round the margin of the disc, in 



the groove separating it from the peristome. 



4. The vestibule is a conical cavity opening exteriorly 



between the ventral margins of the disc and peri- 

 stome. The cilia with which it is provided cause 

 a rapid current oi water to flow in £(,nd out of it. 



If this current he not visihle, run wider the cover-glass a 

 Uttle water containing some insoluble pigment, e.g. carmine 

 or indigo. Indicate the direction of the current in the vesti- 

 bule by arrows on your drawing. 



