372 



BIOLOGY OF THE PROTOZOA 



tylis, Schroder has described myonemes running longitudinally 

 from the stalk to the peristome where they terminate in the basal 

 plates of the membranelles (Fig. 162); distally they combine to 

 form the contractile strand of the stalk. 



£ 



C D 



Fig. 163. — Tentacles of Infusoria. A, Mesodinium pulcx, with four oral tentacles 

 for adhering; B, Podophrya fixa: C, D, tentacles of EpheloticUe. {A, C, D, from Cal- 

 kins; B, Original.) 



A well-defined mouth is present in almost all ciliates (absent in 

 an entire group, only in Opalinidtv. Tn gimnostomata it is closed 

 save at times of food ingestion; in all other groups it is permanently 

 open. In these latter cases the form of the mouth varies from cir- 

 cular to elliptical, crescentic or triangular openings and in the 

 majority of cases leads into a ciliated gullet. Such constant feeders 

 are limited to a bacterial diet and other minute food substances 

 while the gvnmostomes, bv reason of the distensibility of the oral 



