The life of history of Diplofliscns temporatus Stafford. (311 



flattened on one side where is was attached to the substratum. Its 

 "broader end encloses the anterior end of the cercaria. At the 

 narrow, posterior end there is a funnel-shaped orifice where the cyst 

 material extended up about the base of the tail before that organ 

 was broken oft'. 



The cyst is very fragile. It was found impossible to separate 

 a cyst from the side of a glass jar without rupturing- it and allow- 

 ing the worm to escape. 



The encysted cercariae were extremely sensitive to changes in 

 the surrounding medium. When the water in a watch glass in 

 which a number of worms had become encysted was allowed to 

 stand for twenty four hours and was then replaced by fresh water, 

 all of the worms came out of their C3'sts and moved about actively 

 for several hours untill death ensued. 



These young worms which had been in the cyst for twenty four 

 hours diifered from the cercariae in appearence in that they were 

 comparatively much narrower, and lacked the opaque masses along 

 the sides of the body, the cystogenous glands of the cercariae. 



Some experiments were undertaken to determine the ability of 

 the encysted worms to withstand dessication. A number of cercariae 

 were allowed to encyst in each of several small watch crystals. 

 When the cysts were fuUy formed the water was poured off from 

 the dish and the cysts exposed to the air for varying lengths of 

 time. An artificial gastric juice was used to dissolve the cysts after 

 the dessication was over, and in some instances a number of the 

 cysts were broken up with needles and the worms liberated into a 

 dish of water. In all of the experiments a period of dessication of 

 more than one hour proved fatal. The encysted cercariae left in 

 water as a check for each experiment retained their vitality 

 throughout the time of the experiment and all that was necessary 

 in order to cause them to leave the cyst was that the water should 

 be changed in the dish in which they were attached. The evidence 

 gathered in another line of experiments showed that the cysts might 

 remain in the water for at least six weeks and the young worms 

 still be capable of recovering their activity when brought into a 

 suitable environment. 



Pagenstechee (1857) and Reuss (1903) have described a peculiar 

 method of encystment for the cercaria of Bistomum duplicatum. In 

 this form the tail is not used at all as a swimming organ, but con- 

 sists almost entirely of a gelatinnus substance When the cercaria 



