182 



A COURSE ON ZOOLOGY. 



3. The body has a convex dorsal surface and a flat 

 ventral surface carrying cilia; the back is often hard- 

 ened so that the creature much resembles a minute crus- 

 tacean ; examples are euplotes and oxytricha. 



Fia. 110. 



VORTICELLA CONVALLARIA. 



LACRYMARIA PROTEUS. 



4. In this class the body is usually naked, excepting a 

 girdle of elongated cilia, and a spiral of hairs around the 

 mouth. Examples of these are the ophrydmm and the 

 vorticella, The bodies of all the vorticellse are supported 

 by a long contractile stalk. When this is contracted the 

 creature looks like a microscopic flask ; it remains at- 

 tached to a plant, awaiting the passage of some desired 

 prey ; then it elongates its stalk very rapidly, like a 

 liberated spring. 



The figures on pages 180, 181, and 182 illustrate the 

 principal forms that are found in old vegetable infusions 

 and in stagnant water. 



