SUBKINGDOM PROTOZOA. 33 



ceded by the conjugation of two individuals, the combined central proto- 

 plasms coming to the surface of the cyst where they form a protuberance. 

 Repeated division of the nucleus into 2, 4, 8, etc., up to 256 or more now 

 takes place accompanied by only a partial division of the protoplasm, so 

 that the surface of the protuberance is covered by a large number of bud- 

 like structures. Eventually these separate, develop a flagellum, and take 

 on the character of motile spores. Their further development into the 

 adult Noctiluca has, however, not yet been followed. 



IV. CLASS INFUSORIA. 



The Infusoria are tlie most highly specialized of all the 

 Protozoa, showing a differentiation of the protoplasm unat- 

 tained by other members of the group. They are character- 

 ized by the possession during the whole or part of their lives 

 of numerous delicate short motile hair-like processes termed 

 cilia by means of which locomotion is performed and food 

 procured. In one of the orders into which the class may be 

 divided, the CILIATA, these structures are present during the 

 adult life of the organisms, while in the other, the SUCTOEIA, 

 though present in the young stages they are replaced later by 

 immovable processes of the body, which extract the nourish- 

 ment from the food-particles which come into contact with 

 them. 



1. Order Ciliata. 



The Ciliata are for the most part free-swimming organ- 

 isms, though some, e.g. Vorti-cella (Fig. 17, C), adhere to foreign 

 bodies by means of a stalk, similar to that found in Flagel- 

 lates, and colonial stalked forms also occur as in that class. 

 In these stalked forms the body is enveloped in a chitinous 

 case, of which the stalk is a prolongation, the surface oppo- 

 site the stalk being, however, left naked and being surrounded 

 by cilia which are absent on the portions of the body pro- 

 tected by the chitiu (Peritrichous forms, Fig. 17, C). In the 

 free-swimming forms, however, the cilia are more universally 

 distributed, covering either the entire surface (Holotrichous 

 forms, Fig. 17, A) or else one surface of the flattened body, 

 some of them in this case being modified into stout movable 



