174 THE UNIVERSITY SCIENCE BULLETIN. 



This is an exceedingly minute form, measuring only .37 mm. 

 long, including the tail, which is half the length of the body. The 

 width is .03 mm. Both of the suckers are the same size, averaging 

 .015 mm. in outside diameter. This form has a stylet .006 mm. 

 long. On account of the minuteness of this form, the internal 

 structures could not be made out clearly. The best results were 

 obtained by staining intra vitally with picrocarmine. With this 

 stain paired masses of cephalic glands with their ducts could be 

 made out. The tail of this form consists of large cells with a 

 definite single row of nuclei, showing prominently in the median 

 line. 



Sectioning the snails from which these cercariae emerged failed 

 to reveal either sporocysts or redias. 



Seventy-five per cent of hundreds of Planorbis trivolvis collected 

 at Pratt, Kan., August 22, were infected with a small xiphidio 

 cercaria which I propose to call Cercaria kansiensis. The body of 

 this form averages .06 mm. wide and .09 mm. long. The tail in 

 an average state of contraction is .064 mm. long. 



The oral sucker is .024 mm. in diameter and the ventral sucker 

 is .028 mm. The openings in both suckers are .007 mm. in diam- 

 eter. There is a bicomuate groove in the posterior end of the 

 body into which the tail fits. 



No digestive tract could be traced, but a ring of deeply staining 

 cells marks the region of the pharynx. 



Large unicellular cephalic glands are present. They number 

 about four on a side. No ducts could be found leading from them. 



No excretory tubes could be found, but there is a large excre- 

 tory bladder .01 mm. wide and .016 long, posterior to the ventral 

 sucker. The long axis of this bladder is in a transverse direction 

 to the long axis of the body. 



The anlagen of the reproductive organs consist of two masses 

 of cells dorsal to the ventral sucker. The posterior mass is the 

 larger. 



Special studies were made of the stylet of Cercaria kansiensis. 

 It is embedded in the muscles of the thick-walled oral sucker, 

 dorsal to the mouth opening, and can be withdrawn into a hollow 

 receptacle. Two camera-lucida sketches (figs. 57 and 58) show 

 the stylet extended and contracted. The stylet measures .02 mm. 

 in length. At the base and near the point it has a width of one- 

 sixth its length, but between these points it is narrower. 



Cercaria kansiensis is found in sporocysts averaging .33 mm. 

 long and about one-third as wide. 



