166 THE UNIVERSITY SCIENCE BULLETIN. 



The immature cercarise of this species are blunt-tailed and 

 clumsy. No internal organs can be distinguished excepting the 

 eyespots, which are rudimentary. 



The rediae of this form are short and blunt and are provided 

 with anterior and posterior locomotor projections. The digestive 

 tract is short and blunt. The cercariae within the rediae were all 

 immature, due perhaps to the fact that the snail was not fixed 

 until cercariae had ceased to emerge from it. The rediae average 

 .88 mm. long and .25 mm. wide. 



Of twenty specimens of Planorhis trivolvis collected at Lawrence, 

 Kan., July 22, one was parasitized with Cercaria inhahilis Cort. 

 These snails were obtained from the surface of Horseshoe lake, 

 where they were attached to twigs and floating objects. 



The cercariae emerged from the snails that had been isolated in 

 a watch glass, and remained in the immediate vicinity of the snail. 

 Owing to their heavy tails and unwieldy bodies, their attempts 

 at swimming resulted in their floundering about. The creeping 

 motions also were very feeble. When the snail was crushed, 

 rediae and cercariae in various stages of development were found 

 in the liver. A remarkable fact in connection with this species 

 was that the rediae were smaller than the cercariae. 



This apparent inconsistency may be explained by comparing 

 the free cercariae with the sections of the infected snail liver, where 

 free cercariae are to be found completing their development in the 

 digestive gland near the periphery of that organ. 



The length of this species is .76 mm. and the width is .23 mm. 

 There are two prominent pigment spots on the anterior dorsal 

 surface of the body. The digestive tract consists of a slender 

 pharynx leading from the mouth, situated within the oral sucker, 

 to the diverticula of the intestine. The excretory system con- 

 sists of paired tubes opening into the excretory pore just anterior 

 to the ventral sucker. A mass of deeply staining cells, the anlage 

 of the reproductive organs, is anterior to and below the pore. 



The rediae are elongated sacs, the immature ones averaging .55 

 mm. long and .07 mm. wide. The mature ones are slightly longer 

 and twice as wide. The immature forms contain only germ balls, 

 while the mature ones contain both germ balls and developing 

 cercariae that move about within the walls. No mature cercariae 

 were observed within the rediae of this species. 



DiSTOME CeRCAEI^. 



In my material are nine distome cercariae, belonging to five 

 subgroups. 



