PROTOZOA 



47 



mouth there is always a ring of eilia much longer than the rest ; 

 Stentor (Fig. 29), a green, trumpet-shaped, fresh-water animal, 

 belongs to this order. It is visible to the naked eye, and we 

 often see several of them swimming about together, attached at 

 their posterior ends. 



1 3 4 



Fl<;. 29. 1, Stentor polymorphic ; 2, Stylotiickia mytilus, laterai aspect; 3, Aciii- 

 eta fcetida, young individual; 4, Podophrya fixa, young individual. (After 

 Kent.) 



Order 3. Peritricha 



The Peritricha (Gr. 7repi, around, and 6pi%, a hair) have the 

 cilia confined to a spiral band around the anterior end of the 

 body. At the posterior end there is often, but not always, a 

 stalk containing a contractile band by means of which the ani- 

 mal may be drawn toward the object to which it is attached. 

 Vorticella (Fig. 30) is a characteristic representative of the 

 order, occurring in both fresh and salt water. We also find 

 colonies (Fig. 31 ). 



Order 4. Hypotricha 



The Hypotricha (Gr. v-tto, under, and Opi^ a hair) are oval, 

 more or less flattened Ciliata, having one side of the body prac- 

 tically free from cilia, while the other, which may be called the 

 ventral side, possesses cilia and groups of cilia fused together. 



