160 



BIOLOGY OF THE PROTOZOA 



ticularly near the tip, and the cirri then present a most frayed-out 

 or ragged appearance. They vary in size from extremely minute 

 cilia-like marginal and ventral cirri to great ventral brushes in 

 forms like Aspidisca (Fig. 90) or huge hooked structures as in 

 Uronychia, Diophrys and other Euplotidae (Fig. 89) (see also p. 221). 



Fig. 89.— Types of ciliates. A, Perilromus i mmae; B, Kerona pediculus; C, Diophrys 

 appendiculatus; I), Euplotes charon. (A, C, D, after Calkins; B, after Stein.) 



( !irri are preeminently organs of locomotion, but, unlike other 

 motile organs of the ciliates, their stroke is not confined to one 

 plane but may be in any direction. This gives to the Hypotrichida 

 an extreme variety of movements unparalleled by any other group 

 of Protozoa. Many of them walk or run on the tips of their frontal 

 and ventral cirri (Stylonychia) ; others swim with a peculiar jerky 



