MORPHOLOGY 



51 



Stylonychia, etc., walk on f rentals, ventrals, and anals, while swim- 

 ming movement by other species is of different types. 



In all euciliates except Holotricha, there are adoral membranellae. 

 A membranella is composed of a double ciliary lamella, fused com- 

 pletely into a plate (Fig. 12). A number of these membranellae occur 

 on a margin of the peristome, forming the adoral zone of membranel- 

 lae, which serves for bringing the food particles to the cytostome. 

 The frontal portion of the zone, the so-called frontal membrane 

 appears to serve for locomotion and Kahl considers that it is prob- 

 ably made up of three lamellae. The oral membranes which are often 

 found in Holotricha and Heterotricha, are transparent thin mem- 

 branous structures composed of one or two rows of cilia, which are 



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n 



jHOl' 



Fig. 13. Diagrams showing the possible development of a suctorian 

 tentacle from a cytostome and cytopharynx of a ciliate (Collin). 



more or less strongly fused. The membranes, located in the lower 

 end of the peristome, are sometimes called perioral membranes, and 

 those in the cytopharynx, undulating membranes. 



In Suctoria, cilia are present only during the developmental 

 stages, and, as the organisms become mature, tentacles develop in 

 their stead. The tentacles are concerned with food-capturing, and 

 are either prehensile or usually suctorial. In some instances the 

 tentacles are tubular and this type is interpreted by Collin as 

 possibly derived from a cytostome and cytopharynx of the ciliate 

 (Fig. 13). 



Although the vast majority of Protozoa possess only one of the 

 three organellae of locomotion mentioned above, a few may possess 

 pseudopodia in one phase and flagella in another phase during their 

 life-cycle. Among many examples, may be mentioned Dimastig- 

 amoebidae (Fig. 160), Tetramitus rostratus (Fig. 134), etc. Further- 

 more, there are some protozoans which possess two types of organ- 

 ellae at the same time. Flagellum or flagella and pseudopodia occur 



