82 ILLINOIS BIOLOGICAL MONOGRAPHS [82 



cilia (Fig. 145). These cilia come from a flame cell bordering on the lumen 

 of the lateral tube. A second pocket somewhat anterior is an atrium into which 

 many of the capillaries empty; it is filled with small excretory granules, in 

 this way acting as a secondary reservoir. 



The digestive system of C. gracillima consists of an unbranched esophagus 

 without a pharynx sphincter, a pair of short degenerate furcae extending 

 posteriad beyond the acetabulum, and a ring of gland cells in the region of the 

 esophagus where the pharj'^nx might be expected. Opening into the oral 

 atrium thru common bundles of ducts are the salivary-mucin glands (Fig. 144). 

 These glands are very large with vesicular nuclei. They are situated in the 

 posterior third of the body. In cross section the ducts are similar to those 

 described by Cort (1915, Figs. 59-62) for C. douthitti. 



The nervous system has been discussed on page 54. 



The genital cell masses in the cercaria are hermaphroditic (Fig. 149). 

 Anterior to the acetabulum are the vagina and the cirrus pouch buds, and 

 lateral, extending both anteriad and posteriad, are the vitelline follicles. In 

 the posterior extremity is a conical germinal mass, from which are proliferated 

 anteriad a number of small testicular follicles. 



The general features of this fluke make it possible to refer it to the Schis- 

 tosomatidae. 



Cercaria tuberistoma Faust 1917 



This species of cercaria is shorter and much more muscular than C. gracil- 

 lima. The body is elongate ovoid, with the anterior end slightly constricted 

 and crowned with a pair of tuberosities (Fig. 155). The body length is about 

 0.2 mm. and the width 0.05 mm. to 0.06 mm. The tail measures about 0.32 

 mm. as a whole, equally divided into common portion and rami. There is 

 no oral suctorial disc, but instead the oral invertible proboscis. The acetabulum 

 measures 0.03 mm. in diameter. 



The cercaria was secured from a single light infection of Physa gyrina 

 collected in the Bitter Root River at Corvallis, Montana, in October 1916. 

 Out of nineteen snails examined only one was infected. Only a few cercariae 

 were secured, and these were studied as live mounts. From this study the 

 excretory, digestive and general body features were worked out. 



The cercaria develops in an elongate, dumb-bell-shaped sporocyst, spread- 

 ing out at one end to form an attachment disc (Figs. 157, 158). At the end 

 opposite the attachment organ the cercariae develop from the maturation 

 of the germinal epithelium. They escape thru a rent in the wall of the sporo- 

 cyst. Stages in development (Fig. 158, A-E) are similar to those described 

 for C. gracillima (Fig. 143). On the whole the embryos of this species are 

 stouter than those of C. gracillima. 



The excretory system has the features common to all furcocercariae. The 

 bladder and the eyelet are muscular (Fig. 155). The lateral tubes are of 

 small diameter, with anterior and posterior tubules. No anastomoses take 



