o'roke: larval trematodes. 171 



actively. Six hours was the maximum time that these cercarise 

 remained ahve after emerging from the snail. 



The body of this species is .31 mm. long and .125 mm. wide. 

 The main part of the tail has a length of .54 mm., while the 

 branches are .18 mm. long. Two large eyespots are present. 

 They are made up of minute pigment granules and measure .02 

 mm. by .014 mm. in dorsal view, being longer in the transverse 

 direction. 



An excretory tube begins in the branches of the tail and ex- 

 tends throughout the length of that organ to the excretory pore 

 in the posterior end of the body. The excretory tract could not 

 be made out in the body region. 



The branches of the tail are provided with a sort of fin extend- 

 ing around the tip. This fin is beset with minute spines. 



A mouth is present in the oral sucker, but there is no digestive 

 tract leading from it. 



The anlage of the reproductive organs is ventral in position and 

 near the posterior end of the cercaria. 



A peculiar characteristic of this species was that in the fixed 

 specimen the tail is usually bent sharply at its junction with the 

 body. 



The redise of this species average .2 mm. long and ,11 mm. wide. 

 They are filled with germ balls and cercarige in various stages of 

 development. The anterior end is somewhat pointed, while the 

 posterior end is rounded. 



Cercaria echinocauda is similar to Cercaria ocellata La Valette 

 St. George, as the measurements for this species fall within the 

 wide range described for Cercaria ocellata. Both forms are pro- 

 vided with fin-like projections on the tail. The tail of Cercaria 

 echinocauda is not very contractile, contrasting with that of 

 Cercaria ocellata. The oral sucker of Cercaria echinocauda is also 

 much larger than that of Cercaria ocellata. Cercaria echinocauda 

 develops in rediee, while Cercaria ocellata is found in sporocysts. 



Of thirteen specimens of Plariorbis trivolvis collected at Law- 

 rence, Kan., October 7, two were infected with a cercaria for 

 which I propose the name Cercaria quieta, because of its often 

 remaining motionless, floating in the water for brief periods of 

 time. Like Cercaria inversa, this cercaria has a bifurcated tail 

 and swims by means of a rapid vibratile motion of this organ. 



The tail is enormous in size compared to the body and is not 

 constricted off from the body in the living specimen as is the case 

 with other furcocercous forms. The tail of this species is never 



