Branch Protozoa 13 



temporary processes. The Amoeba is a typical example 

 of this class, having a nucleus, nucleolus, and contractile 

 vacuole. Under unfavorable conditions the Amoeba may 

 become encysted and remain in that condition for a long 

 time. Many Rhizopods are marine, secreting a covering 

 or shell of carbonate of lime. The shells, falling to the 

 ocean bottom when the animals die, in the course of geo- 

 logic ages form vast areas of rock. Some of the most 

 important animals carrying on this work are members of 

 the order Foraminifera. 



The second class, Mycetozoa, consists of a group of 

 organisms which are often included by botanists among 

 plants, and called "slime-fungi." They so combine the 

 characters of animals and plants that it is very difficult 

 to say definitely to which kingdom they belong. They 

 live upon decaying organic matter — such as leaves or 

 damp wood, where they appear spread out in thin sheets 

 of jelly-like protoplasm. 



The Euglena is a typical example of the third class, 

 Mastigophora. The members of this group were formerly 

 united with the Paramecium and similar animals to form 

 the class Infusoria. Now, however, those creatures fur- 

 nished with flagella are included in the Mastigophora. 



The fourth class, Sporozoa, consists of microscopic 

 creatures living as parasites within other animals. The 

 best known examples belong to the order Gregarinida, 

 and live in the intestines of various insects and other 

 Arthropods and worms. 



The members of the fifth class, the Infusoria, repre- 

 sent the highest Protozoa. In these the protoplasm of 

 the cell is generally differentiated on the outside into a' 

 somewhat hardened covering, inside of which is the more 

 fluid protoplasm. All the members of this class are pro- 



