CORTICATA. 



PHYJLUM CORTICATA. 



The CoRTiCATA contain the important class Ciliata, of 

 which ParamcEcium and Vorticella are typical. They are 

 all active organisms, those like ParamcEcium moving rapidly 

 in pursuit of prey, whilst others like Vorticella are themselves 

 fixed and use their cilia to bring food-particles to them. 

 They are divided into orders according to the arrangement 

 of the cilia. 



The second class is that of the Mastigophoka. They 

 are also small active organisms, often of very minute size. 

 They have only one, or sometimes two, long whip-like 

 processes which' are called 7f^^^//<3J. The flagellum maybe 

 situated at the posterior end and serve to drive the body 

 forwards, in which case it is called 2i pulsellum, or it may be 

 at the anterior end and may draw the body after it, when it is 

 known as a tradellum. The tractellum may also by spiral 

 movements assist in bringing food to the mouth. 



In one large section of these Mastigophora, often 

 placed in a class by themselves, the Choano-Flagellata^ the 

 ingestive action of the tractellum is supplemented by a 

 "collar" of protoplasm which surrounds the mouth and the 

 base of the tractellum Colonial forms are common in 

 this class. 



The AciNETARiA are a spe- 

 cialised class of much the same 

 general habit of life as the pre- 

 ceding classes, but there are no 

 cilia nor flagella. Their place is 

 taken by a number of fine pro- 

 cesses terminating in minute 

 suckers or adhesive discs with 

 which other Protozoa are caught 

 and their juices extracted. Most 

 are fixed and stalked, but some 

 are free and even parasitic. The 

 young are often actively ciliated, 

 and the whole class is probably 

 derived from ancestral Ciliata. 



Fig. 36. — Act N eta Tu- 

 BEROSA Expanded and 

 Contracted. 



