94? ELEMENTARY BIOLOGY. [IX. 



B. Other forms closely allied to Vorticella which may be 

 . met with, and which will do nearly as well for exami- 

 nation, are ; 



a. Epistylis. Bell-shaped animals growing on a 

 branched non-contractile stalk. 



b. Carchesium. A form very like Vorticella but borne 

 on a branched contractile stalk. 



C. Cothlirnia. An almost sessile form, provided with 

 a cup or envelope into which the bell can be re- 

 tracted. 



[The activity of the movements of the free Infusoria interferes 

 with the complete examination of the living animal. It is well 

 therefore to add a little osmic acid solution to the drop of water 

 under examination. This kills such Infusoria as Paramcecium, 

 Nyctotherus and Balantidium instantly, without destroying the 

 essential features of their organization.] 



