768 DR. WILLIAM NICOLL ON 



suspended in water, a continuous shower of larvpe was observed to 

 fall to the bottom of the vessel. 



The first form, which I name Cercaria ordinata, sp. n. (text- 

 fig, 107 a), was much more numerous than the other. It is a 

 typical tailless encysted cercaria, about "5 mm. (•4-'55 mm.) in 

 length and •2-*25 mm. in greatest breadth. In shape it is ovoid 

 and flattened dorso-ventrally. The entire surface of the body is 

 covered with minute regularly-arranged spines. The oral sucker 

 is almost terminal and has a diameter of "07 mm. (•06--08 mm.). 



Text-fie-. 107. 



\ 



^ 



\ 



A 3 



A. Cercaria ordinata, sp. ii. Ventral view, X 150. 



B. Di]plostomum sirtale, sp. ii. Ventral view, X 150. 



The length is usually slightly greater than the breadth, and the 

 sucker has a somewhat characteristic funnel-shaped appearance. 

 The globular ventral sucker is situated rather in front of the 

 centre of the body, and has a diameter of "083 mm. (•075-'097mm.). 

 Its distance from the anterior end of the body is on an average 

 "22 mm. (•17-'25 mm.). On the dorsal lip of the oral sucker are 

 the two symmetrical apertures of the cystogenous ducts. The 

 ■cystogenous glands are conspicuous structures, and consist of four 



