THE PROTOZOA. 137 



more or less jelly-like exterior prolonged into tem- 

 porary or stationary branches (pseudopodia), they have 

 a firm, almost membranous exterior, and they move by 

 means of cilia. Cilia are short processes of proto- 

 plasm, which are usually placed in rows. They have 

 an active vibratory movement, by which a current 

 is created in the surrounding water. A long un- 

 branched process, called a flagellum, is also borne by 

 some Infusoria. The Infusoria have always a contrac- 

 tile vacuole, and many forms have a mouth. They 

 are divided into two oi'ders, the Flagellata, or Monads, 

 and tlie Giliata. The former are so called because 

 their distinctive feature is the possession of a flagellum : 

 some forms have two. These abound in infusions of 

 decaying organic matter, and some kinds especially 

 in infusions of decaying fish. The stage which has a 

 long flagellum is called a mastigopod (whip-footed 

 animal). Some forms of this sort have been seen to 

 issue in numbers from an encysted parent form. In 

 some cases these young mastigopods develop after- 

 wards into an amceboid stage. Sometimes several of 

 them fuse to form an amceboid body. The non- 

 nucleated Flagellata are placed by Haeckel in a group 

 called Monera (Monads). 



The amoebiforra stage is sometimes referred to as a 

 myxopod (jelly-footed animal, i.e. one with pseudo- 

 podia). The position of this group, and of individual 

 members of it, is not very certain ; for some of the 

 animals assigned to it may not be adult forms, and 

 some of the compound amoeboid forms may be only a, 



