THE PROTOZOA 



Do these organisms grow old and die unless they are "rejuvenated" by conju- 

 gation? In some species such a rejuvenescence seems to occur, if the experi- 

 mental evidence cannot be accounted for on other grounds. At the very least, 

 conjugation, like other kinds of sexual reproduction, provides for a species 

 the advantages of new nuclear combinations which make for greater vari- 

 ability and adaptiveness. 



Other Ciliates. The class Ciliata includes most of the species of large 

 Protozoa occurring commonly in fresh water; therefore, this class will be 

 reviewed by listing its principal subdivisions and the names of representative 

 genera; some of the forms listed are illustrated in Figure 8.24. 

 Class Ciliata 



Subclass Protociliata — cilia of equal length covering entire cell; leaf-shaped or 

 ellipsoidal in shape; no cytostome; parasitic in intestine of amphibians and 

 fishes. Opal ma and Protoopahna. 

 Subclass Euciliota — ciliation and shape of cell specialized as indicated in the 

 several orders; typically free-living, but some species in each order parasitic. 

 Order Holotrichida — cilia of approximately equal length and uniformly cover- 

 ing the cell in most species; with or without a cytostome; without a 

 special adoral zone of cilia. AmphUeptus, Coleps, Colpoda, Didimum, Dtleptus, 

 Frontoriia, Lacrymana, Lionotus, Paramecium, Prorodon, etc. 

 Order Heterotrichida — cilia of cell surface small or reduced in numbers as 

 compared with the specialized ciliation of the oral region. Nyctotheriis, 

 Spirostomum, Stentor, etc. 



Euplotes 



Lacrymaria 

 Q,!jt Spirostomum 



Lionotus 

 Fig. 8.24. Representative ciliates. 



257 



