STRUCTURAL DIFFERENTIATIONS 



135 



throughout their length to the cortex while the axial thread forms 

 the contractile margin (Fig. 97, p. 212). Such vibratile mem- 

 branes are characteristic of the genera Trypanosoma, Cryptobia, 

 Trichomonas, Trichomastix, etc., all of which are parasites in the 

 blood or digestive tract of different animals. 



Fig. 69.— Free-living flagellates with trailing flagella. A, C, D, Bodo cmidalus St. 

 B, Bodo glohosus St.; E, Ploeotia vitrea Duj. (After Calkins.) 



