o'roke: larval trematodes. 167 



megalurous cercari^. 



Of twenty specimens of Planorhis trivolvis collected at Lawrence, 

 Kan., July 27, one was infected with Cercaria viagnacauda. This 

 is an active free-swimming form, positively phototropic. It did 

 not undergo creeping motions excepting when the tail was de- 

 tached from the body. 



The behavior of this cercaria was noted carefully. They would 

 swim actively for a few minutes, then come to rest, pointing head 

 downwards at an angle of fifteen degrees from the vertical. In 

 this position the tail is blade shaped and flattened dorsoventrally. 

 Practically all of the cercarias would be either resting or swimming 

 at any one time. These cercariae were especially virile, living 

 from thirty to forty-eight hours after emerging from the snail. 

 The tail invariably became detached from the body and continued 

 swimming after the death of the former. This form did not encyst. 



The rediae of this species were found in tangled masses in the 

 liver of the host. They average .9 mm. long and from .1 mm. to 

 .5 mm. wide, having a short digestive tract. The mouth is ter- 

 minal and well defined, being provided with a large median stylet. 



This remarkable cercaria has a total length of 1.56 mm., the 

 body comprising only .127 mm. leaving it less than one-eleventh 

 of the length of the tail. These measurements, which were taken 

 from balsam mounts, are approximately normal, excepting that 

 the tail is somewhat flattened. 



From a study of the living material only the suckers and the 

 concretions in the excretory ducts could be seen. Mounted speci- 

 mens show the enormous excretory tract and the reproductive 

 anlagen, while the cephalic glands can be seen in sections. 



The excretory tract consists of two tubes extending from near 

 the oral sucker to a large excretory bladder, posterior to the ven- 

 tral sucker. This bladder communicates with another in the an- 

 terior narrow part of the tail. Opening into this secondary bladder 

 is the median excretory duct of the tail, which is ventral in posi- 

 tion. 



The reproductive anlagen appear as two masses of cells anterior 

 and posterior to the ventral sucker. No digestive ti-act could be 

 traced. 



The oral sucker is .007 mm. in outside diameter, while the ven- 

 tral sucker is twice this size. The tail is made up of large paren- 

 chymous cells and longitudinal and cross-muscle fibers. Owing to 

 its delicate structure it could not be embedded for sectioning. 



