28 



HANDBOOK OF PROTOZOOLOGY 



The flagellum is usually inserted near the anterior end and 

 directed forward. Its movement will pull the organism toward 

 the front. Combined with this there may be a trailing flagellum 

 which, as the name implies, is directed posteriorly. It serves to 

 steer the course of movement or it may push the body forward 

 to a certain extent. In a small number of flagellates, the 

 flagellum is inserted near the posterior end of the body. In such 

 cases its movement will push the body forward. The pulling 

 and pushing flagella were called tractella and pulsella, respec- 

 tively, by Lankester. 



In some parasitic Mastigophora such as Trypanosoma (Fig. 

 5), Prowazekella (Fig. 5), Trichomonas (Fig. 61), etc., there is 

 a very delicate membrane along one side of the body and la 

 flagellum makes its outer margin. \\'hen this membrane vi- 

 brates, it presents a characteristic undulating movement, as will 

 easily be seen in Trypanosoma rotatoriiim. This structure is 

 called the undulating membrane. 



Cilium 



Pore for cilium 



'^^(^^«=*'5^j;^^-^ End-view of trichocyst 



Membranellae 



Basal line composed of 

 basal granules 



Peristome fibril 

 Basal lamella 



End fiber 



Fig. 9 a. Part of the pellicle of Paramecium caudatum, showing the arrange- 

 ment of cilia. XI 100 (After Schuberg) 

 b. Portion of the adoral zone of Stentor coerideus showing three mem- 

 branellae. (After Dierks). 



Cilia are the cell-organs of locomotion found chiefly in the 

 Ciliophora. They are fine and short cytoplasmic projections and 

 originate in the ectoplasmic portion of the body (Fig. 13). 

 Ordinarily they are very numerous in holotrichous ciliates and 

 uniform in length, as in Opalina, or they may be longer at the 

 extremities, in the peristome or around the cytostome. They 

 undergo alternate movements of contraction and relaxation. 

 Some investigators believe that there is a layer of contractile 

 element at one side of the axial filament which arises from a 

 minute granule embedded in the ectoplasm, and that its contrac- 



