o'roke: larval trematodes. 163 



One lot was allowed to dry for forty-eight hours, being kept in 

 a covered watch glass. The air was moist, but there was no water 

 covering the cysts. The cysts were covered with water and later 

 opened. The cercariag were alive and active. Longer and more 

 complete desiccation proved fatal to the cercariae. 



The process of encysting was carefully noted for this species. 

 The swimming ceases; the anterior end of the body is directed 

 downwards or towards the side of the container; the oral sucker 

 becomes attached; the tail vibrates rapidly, then the cercaria 

 loosens its hold and goes through creeping motions, but does not 

 swim any. This process is repeated a few times, then the cercaria 

 flattens itself against the glass and assumes a spherical shape. 

 The head is twisted from side to side within the cyst wall, and the 

 tail continues to vibrate. The worm becomes more transparent 

 and the cercaria seems to loosen from the outer wall, which as- 

 sumes a furry appearance, due to the giving off of cystogenous 

 material by the cystogenous glands. At this time, the cercaria 

 begins peculiar rotating movements, which continue from an hour 

 and twenty minutes to two hours and ten minutes. The motion 

 consists of a series of intermittent movements. The time required 

 for a cercaria to make a complete turn varied from one and three- 

 fourths minutes to two and a half minutes, with from thirteen to 

 twenty-two separate movements in a revolution. 



The cyst wall becomes thicker and more transparent. Some- 

 times the tail loosens and swims away, while at other times it may 

 remain loosely attached to the cyst. One tail vibrated constantly 

 for eight hours after the cercaria began to encyst. The tail as 

 well as the body gives off cystogenous material, which is in the 

 form of a delicate sheath surrounding that organ and at a distance 

 of one-half the width of the tail from it. 



The motions of the encysting cercaria become slower and slower, 

 and finally cease as the process is completed. When the cyst is 

 fully formed it is much more transparent than the free-swim- 

 ming cercaria, and the worm is coiled within the cyst with its 

 anterior and posterior ends in contact. Slight spasmodic motions 

 within the cysts can be noted for three or four days after encyst- 

 ment. Sometimes the cercaria breaks out of its cyst by rupturing 

 the wall, and forms a new cyst. The cercariae usually encysted 

 on the bottom and sides of the watch glass nearest the window, 

 and were shaped like a deep plano-convex lens. In a few cases 

 where encystment took place among masses of snail faeces and 



