164 THE UNIVERSITY SCIENCE BULLETIN. 



not against the side of the container, the shape of the cysts was 

 ellipsoid. 



Cercaria cortii is a rapid swimmer, and its swimming motions 

 are strikingly regular. It would often propel itself in a straight 

 line from one side to the other of a Syracuse watch glass. Creeping 

 motions were rather infrequent in open water, but under the cover 

 slip this was the usual method of locomotion. 



The measurements of this cercaria were taken from preparations 

 mounted in glycerine and glycerine jelly after the specimens were 

 killed by heating slightly, and represent as accurately as possible 

 the size of the form in life. 



This cercaria is elongate, oval, and wider at the posterior than 

 at the anterior end. It is capable of assuming shapes varying 

 from spherical to long and narrow. The length of the body is .94 

 mm. and the length of the tail is .87 mm.; a total length of 1.81 mm. 

 The width of the acetabulum is .25 mm. and the width of the oral 

 sucker is .08 mm. The edge of the oral sucker presents a finely 

 lobated appearance. 



The mouth is situated within the oral sucker and opens into an 

 oral cavity .01 mm. wide and .06 mm. long. This is separated 

 from the esophagus by a constriction. The esophagus narrows 

 into a pharynx about one-third the diameter of the oral cavity. 

 It is surrounded by a band of longitudinal muscle fibers .027 mm. 

 in outside diameter. The width of the digestive diverticula is 

 .017 mm. 



Fig. 2, a cross section through the region of the eyespots, shows 

 the brain. The nerve cords could not be traced any distance from 

 this region. 



The anterior one-third of this cercaria is heavily pigmented 

 with dark pigment. 



The esophagus is long and narrow. The digestive tract extends 

 five-sevenths of the length of the body. The two eyespots are 

 prominent and are .028 mm. in diameter and .16 mm. apart. The 

 tubes of the excretory system extend from near the eyes to just 

 in front of the acetabulum. 



The excretory tubes are made up of large flame cells, irregularly 

 joined together, and very closely associated with the digestive 

 tract. In the living form these tubes appear to be cylindrical and 

 rather regular in shape, but cross sections of the fixed specimens 

 (fig. 3) show the true nature of these ducts. In some places they 

 seem to take a spiral course around the diverticula of the diges- 

 tive tract. These cells contain concretions .007 mm. in diameter. 



