288 ZOOLOGY 



The attachment of Stentor to objects is not permanent, for it 

 ma}' loose its holtl and swun free. When the animal is stained 

 in hgematoxylin, the characteristic nucleus, looking like a chain 

 of beads, becomes evident. 



The bell-animalcule (Vorticella) is found in pools or infu- 

 sions, permanently attached by a long stalk. When the ani- 

 mal is irritated, it contracts its stalk, which twists into a close 

 spiral. In other species, colonies are formed, so that a num- 

 ber of heads is attached to a central stalk (Fig. 273). A 

 colony, when fully expanded, appears like a fine, white mould 

 attached to a suljmerged object. In both of these tj'pes the 

 food con.sists of small organic particles, which are swept 

 into the gullet by the circlet of cilia placed around the upper 

 end of the body. 



The Suctoria are sessile Infusoria, from whose upper surface 

 nmiierous remarkable sucking tentacles arise. By means of 

 these tentacles the animal can hold on to Paramcecia and 

 other free-swimming Infusoria, from which it extracts the 

 body fluids. Some Suctoria are stalked, while others are un- 

 stalked. They are found most abundantly in standing water, 

 either fresh or salt, and are often attached to other animals, — 

 Bryozoa, entomostracans, and pulmonale moUusks. 



