INFUSORIA. 147 



species, the bodies of all being somewhat changeable in 

 form. The largest ones are trumpet-shaped, and are 

 usually attached to some object by the narrow .end of 

 the body. They also commonly form a soft, brownish, 

 granular sheath or lorica, to the bottom of which they 

 retreat when disturbed, folding together the wide trum- 

 pet-shaped front border. The entire surface of the body 

 in all the species is ciliated, but the cilia are very small 

 and fine. Around the edge of the front border is a cir- 

 cle of longer and larger vibratile hairs, visible with a 

 moderately low power. The Stentors are all common. 

 The following Key may help the beginner to recognize 

 some of those most frequently seen. 



Key to some species of Stentor. 



1. Attached, and usually forming a short, soft sheath (a). 



2. Free-swimming, more or less ovoid ; green, red, blue 



or almost black (J). 



a. Body large, trumpet-shaped, greenish 

 often without a visible sheath, and 

 when one is formed it is sometimes 

 soon abandoned, the Stentor swim- 

 ming about freely. The body is 

 slightly changeable in shape. Sev- 

 eral Stentors of this species are often 

 found close together, having formed 

 a very soft sheath divided into irreg- 

 ular compartments, one for each Infusorium. S. 

 polymorphus. Fig. 114:. 



