o'roke: larv.\l trematodes. 169 



into a very slender shape. The infection was slight, and these 

 studies were made entirely from the li\ing material and two 

 mounted specimens. 



This cercaria is exceedingly active and is capable of extending 

 the body until it is as narrow as the tail. This form can also ex- 

 tend the ventral sucker until it appears prominent in a lateral view. 

 In a characteristic position this form is slender, heart-shaped. 

 The oral sucker is minute, the ventral sucker being four times as 

 large. 



The esophagus is slender and has a fold near the anterior end. 

 Just beneath the fold is the nan'ow phar^Tix. 



The diverticula of the digestive tract are broad, encircling the 

 ventral sucker. The excretory- system could not be made out, but 

 paired rows of cells with highly refractive nuclei, or possibly con- 

 cretions, mark this tract. The tail is broad and large, being one- 

 third the width of the body and a little over twice the length of 

 the same. The entire length of this cercaria is .53 mm. 



The redice are of imusual shape, tapering at both ends with a 

 definite collar near the anterior end. The digestive tract is slen- 

 der, extending about half the length of the body. Within the 

 rediae are germ balls, developing cercariae. and mature cercariae. 

 The dimensions of the redise are 1.6 mm. long and .33 mm. wide 

 in the widest place. 



FURCOCERCOUS CERCAJILE. 



Two per cent of large numbers of Pkysa gijrina, 436 in all, col- 

 lected at Lawrence, Kan., during the months of July and August, 

 from Haskell pond and the lake at Lakeview, were parasitized 

 with a form for which I propose the name Cercaria inrersa, be- 

 cause of its being directed tail foremost in swimming. The cer- 

 cariae emerged freely from the snails and flitted about rapidly in 

 the water with a peculiar \-ibratile motion, dii-ected tail foremost. 

 Creeping movements were not obsei'\'ed excepting under the cover 

 slip, when the tail became severed from the bodj'. WTien the 

 parasitized snails were crushed, rediae containing cercariae in all 

 stages of development, from mere germ balls to mature forms, 

 were present. The various stages in the development of the cer- 

 cariae could be easily obser^'ed because of the characteristics of 

 the tails, which varied in length from mere stubs and rounded 

 lobes to the elongate btfui'cated tails of the matui'e forms. 



The rediae* were in a tangled mass in the liver. The largest 



* Further studies showed that the rediae of this species may be four times as long as the one 

 shown in figure 47, and much constricted, resembling link sausage. 



