CORTICATA. IOI 
PHYLUM CORTICATA. 
The Corticata contain the important class Cruiata, of 
which Paramecium and Vorticella are typical. They are 
all active organisms, those like Pavamecdum moving rapidly 
in pursuit of prey, whilst others like Vordice//a 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 MasticopHora. 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 /age//a. The flagellum may be 
situated at the posterior end and serve to drive the body 
forwards, in which case it is called a pu/seZ/um, or it may be 
at the anterior end and may draw the body after it, when it is 
known as a ¢ractellum. he ¢ractellum may also by spiral 
movements assist in bringing food to the mouth. 
In one large section of these MasticopHora, often 
placed in a class by themselves, the Choqno-Flagel/ata, 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- Fig. 36.—AcINETA Tu- 
cialised class of much the same BEROSA EXPANDED AND 
general habit of life as the pre- CONTRACTED. 
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 CrLiaTa. 
