128 University of California. Publications in- Zoology [Vol.20 



to have the same relation to the neuromotor system that the right 

 axostyle has in the neuromotor system of the right side of Giardia. 

 "We have called it a para.style because it is alongside the cytostome. 

 It differs from the axostyle of Cfiardia, in not ending in a free flagellum. 

 The parallelism in the persistence in the cysts of Giardia of axostyles 

 and parabasals and of the parastyle and parabasal in Chiloniastix 

 is significant of the homology of these structures in the two genera. 



The flagella of Chiloinastix are four in number and fall into three 

 categories, the two left anterior (fig. A, /. a. fl.), the right anterior 

 (r. a. ff.) and the cytostomal {cyt. fl.). The three anterior ones are 

 free throughout their whole course, while the fourth is attached to 

 the cytoplasm and proceeds posteriorly within the cytostome as an 

 undulating membrane. The two left anterior flagella arise from the 

 primary blepharopla.st. In locomotion these two flagella act in 

 unison, beating together in the backward stroke, the wave of con- 

 traction in the inner one slightly preceding that in the outer one. 

 These two flagella are thrown down against the left side of the body 

 while the right anterior one beats in the opposite direction and is 

 thrown down against the right side of the body with a tendency to 

 lie for a time in a trailing position. It arises from the secondary 

 blepharoplast. The length of these three anterior flagella is about 

 equal to the length of the body. 



The cytostomal fiagellum. (fig. B, cyt. ft.), or undulating membrane, 

 originates from the tertiarj^ blepharoplast and runs posteriorly in the 

 floor of the oral pouch within the cytoplasm to or near to the end 

 of the cytostome. In action it moves in rapid waves of contraction 

 running posteriorly and almost equalling the width of the oral pouch 

 in amplitude. The rate, in moribund individuals whose quiescence 

 permits observation, is two to four beats per second. The amplitude 

 of the lateral movement dies out distally. We have never been able 

 to see any evidence of a free end of this flagellum. The fiber which 

 constitutes it persists in the encysted stage and can be traced by 

 careful focussing. 



This flagellum corresponds to the filament in the margin of the 

 undulating membrane of Trichomonas, Trichomitus, and Eutricho- 

 mastix, the cytostomal flagellum of Chilomastix being, in reality, a 

 diminutive undulating membrane enclosed in the cytostomal pouch. 

 It lies adjacent to the parabasal the location and length of which are 

 correlated with those of this flagellum, as in the triehomonad flagel- 

 lates. Its presence has led to confusion of Chilomastix with Tricho- 

 monas in many clinical accounts of human flagellates. 



