19. 



(fig. 130) arranged in a definite plan. Again Loose (1892, 

 pi. XX, fig. 9) shows "Amphistomura subclavatum 11 to be 

 bilateral, having two flame cells on a side. Cort (1918c, 

 pi. VII, fig. 2) also finds Ceroariaeuni mutabile_ to be 

 bilateral ind as far as he oould make cut, with definite 

 capillary arrangement. Prom this evidence it seems con- 

 servative to say that probably the excretory systems in all 



m 

 rediae are bilaterally syi^triaal and may have a definite 



grouping of the capillaries and flame cells* 



, ?)<j? Tf ^: " 



The fully developed cercaria of ^chinos to ma revolutuia 

 has a total length of from 0.82 to 1*2& mm. , according to 

 the degree c f contraction, averaging about 1 mm. when 

 moderately extended and frrm 0.19 to 0.3C mm. in width, 

 averaging about 0.25 mm. at its widest part. The body 

 alon^ varies from 0.39 to 0.63 mm. 'depending on the aracunt 

 of contraction; the tail from 0.43 to 0.62 mra. depending 



V f 



on the same condition. Occasionally in extreme contraction 

 or expansion of the body and tail there is an even greater 

 range of variation. Generally the length of the body and 

 tail are about equal when moderately extended, each being 

 about 0.50 ram. The width of the tall under average extension 

 is about 005 mm. at the widest point. Actual variation in 

 the size of bercariae is not observable, the difference being 

 due entirely to the degree of contraction. The ventral sucke 



is somewhat larger than the oral sucker; the former meaaur- 



-;', 

 ing on the average 0.094miEtt and the latter 0.072 mm. When 



seen from the side the ventral aueker is often to be found 

 greatly extruded (fig. 44). It is located just back 



