172 THE UNIVERSITY SCIENCE BULLETIN. 



severed from the body in the hving form, and only rarely did it 

 become lost during mounting. 



The cercaria can swim either forwards or backwards. The tips 

 of the bifurcated tail are fitted with adhesive organs by means of 

 which they attach themselves to the substratum or other cer- 

 carise. Both oral and ventral suckers are small and of uniform 

 size, measuring .027 mm. in diameter. 



The excretory system consists of paired ducts leading from the 

 anterior end of the body to the junction of the body and tail, 

 where they anastomose and extend on back to the excretory pore 

 which opens between the forks of the tail. No excretory vesicle 

 is present but the excretory tube is somewhat dilated just anterior 

 to the excretory pore. 



The anlage of the reproductive system is posterior to the ven- 

 tral sucker. No digestive tract could be traced. 



The total length of the cercaria is .8 mm. and the width is .08 

 mm., the main part of the tail being as wide as the body. Of 

 the total length the body makes up one-fifth, the unbranched tail 

 two-fifths, and the branched tail two-fifths. 



The redia of this species is long and cylindrical, measuring 1.52 

 mm. by .2 mm. Each redia contains many cercarise, about one- 

 fifth of which are mature. The rediae were so tangled in the 

 liver that it was almost impossible to dissect them out entire. 



XIPHIDIO CERCARIA. 



My material contains three species of xiphidio cercariae. Owing 

 to the extreme difficulty of studying these small forms, my de- 

 scriptions are in some places incomplete. I am unable to make 

 these species fit in with previously described forms, much as they 

 resemble forms described by Cort and Luhe. 



For the first of these species I propose the name Cercaria has- 

 kelli, from the locality where it was found (Haskell pond). One 

 of thirty-three specimens of Physa gyrina collected from this 

 locality at Lawrence, Kan., July 12, was infected with this species. 



Cercaria haskelli is a rapid swimmer, the swimming alternating 

 with creeping movements. A marked characteristic of this species 

 was that it could extend the tail until it was three or four times 

 the length of the body. When this form was swimming, the body 

 would be contracted into a ball and the tail would be very much 

 extended. 



The measurements for this species in an average state of con- 

 traction are, length .15 mm. and width .05 mm. The tail meas- 



