42 ILLINOIS BIOLOGICAL MONOGRAPHS [488 



numbers were freed when the organ was removed from the snail. Also in 

 the body cavities of numbers of the same snails were found encysted cer- 

 cariae of the same species. That the cercariae were continually making 

 their way out and encysting in new snails was shown by the fact, that 

 while during the first few days after the snails came into the laboratory 

 only a few contained the encysted cercariae, later all were infected. 



The movement of Cercaria reflexae both in open water and in a 

 substratum was exactly like that of Cercaria trivolvis. 



The body varied greatly in size and shape. "When contracted for 

 locomotion it was nearly as wide as long. A fairly well extended 

 mounted specimen (Fig. 43) is pointed anteriorly, widest at about the 

 level of the acetabulum and narrower at the posterior end. The anterior 

 end does not suggest the echinostome collar, and there is no crown of 

 spines. One well extended specimen had a length of 0.46 mm. and a 

 width at the acetabulum of 0.135 mm., with a thickness of a little more 

 than half the width. 



The tail at average extension has a length a little greater than the 

 body, and an average width at its base of 0.05 mm. to 0.06 mm. The 

 tail is provided with a dorsal and a ventral fin-like ridge which is nar- 

 row at its base and at its widest part equals about one-half the diameter 

 of the tail. 



The oral sucker has a diameter of 0.046 mm. and the acetabulum 

 which is just back of the middle of the body is 0.06 mm. in width. 



The surface of the body back to the region about half way from the 

 acetabulum to the posterior end is covered with small spines arranged 

 in rows and set closely together. 



The whole body from the oral sucker to the posterior extremity 

 contains large unicellular cystogenous glands which open dorsally, and 

 fill the bulk of the body toward the dorsal side. These are like the 

 cystogenous glands already described for Cercaria megalura and the 

 amphistomes. 



The oral cavity is followed by a short prepharynx and a small 

 pharynx, 0.022 mm. in diameter. The esophagus and the intestinal ceca 

 were very small and could only be followed in sections. The esophagus 

 reaches almost to the acetabulum and the intestinal ceca to the posterior 

 end. 



The excretory system of Cercaria reflexae (Fig. 43, ex) is very 

 much like that of Cercaria trivolvis. In the former species the vessels 

 from the bladder to the tail are larger and serve to carry away the 

 excretory products, for when the excretory bladder became contracted 

 they became distended but soon again became reduced. The excretory 

 crura too are smaller than in the other species. Opening into the 



