58 ILLINOIS BIOLOGICAL MONOGRAPHS [504 



caliber and club-shaped ends protruded from the mass. They were very- 

 much twisted together and none of the individual sacs were disentangled 

 without breaking. The jutting ends moved slightly, swaying backward 

 and forward. 



Thruout their whole length the sporocysts (Fig. 77) were stuffed 

 with cercariae of different ages, and mature forms in large numbers 

 wormed out of the broken places in the sporocysts. The swimming 

 movement of the cercaria offered nothing peculiar and since the oral 

 sucker did not appear to function, creeping was not very effective. 

 The name Cercaria hemilophura is proposed from the fact that a fin- 

 like projection extends for half the length of the tail. 



Cercaria hemilophura (Fig. 76) is oval elongate in shape and widest 

 at about the middle. The average length in well extended mounted 

 specimens is 0.38 mm. and the width 0.14 mm., with a thickness of about 

 one-half the width. 



The tail at average extension is about the length of the body, 

 0.36 mm. being the average in toto mounts and with a width of 0.048 

 mm., but it can be extended to almost twice that length. Along the 

 ventral surface of the posterior half of the tail extends a fin-like projec- 

 tion, which at its widest is about half the width of the tail. 



The oral sucker has a length of 0.065 mm. and the acetabulum, 

 which is just back of the middle of the body, has a diameter of 0.049 mm. 



The stylet (Fig. 75) is small, tapers regularly to a point and has 

 no thickened region. It measures 0.020 mm. in length and 0.005 mm. 

 in width at its base. 



The whole surface of the body is covered with very small cuticular 

 spines pointing backward, which are very dense in the preacetabular 

 region but thin out slightly posteriorly. They are contained entirely 

 within the thickness of the cuticula and have a length of from 0.0055 

 mm. to 0.0065 mm. 



The whole body contains large numbers of small cystogenous glands 

 filling almost all the available space. 



Stylet glands could not be distinguished. 



The digestive system of Cercaria hemilophura is very clearly differ- 

 entiated. The oral cavity is followed by a very short prepharynx and 

 a good sized pharynx 0.033 mm. in diameter. From the pharynx a large 

 esophagus reaches back almost to the acetabulum. The esophagus is thin 

 walled but the intestinal ceca are lined with cuboidal cells which at this 

 stage fill most of the lumina. 



It was possible in many cases to trace the branches of the excretory 

 system to the flame cells. The bladder is club-shaped, extending about 

 three-fourths of the distance from the posterior end to the acetabulum, 



