610 L. R. Cakv. 



of the cercariae were moving about within the body cavity of the 

 redia in a perfectly normal manner. 



In order to provide more nearly similar conditions the following- 

 experiment was also undertaken: One lot of rediae were teased out 

 in a dish of water, those of the other lot were also separated from 

 the liver of the snail, but were put into a liquid obtained by 

 crushing the livers of uninfected snails. In this experiment the 

 results were similar to those obtained in the one last described. 

 The cercariae in the rediae exposed to the water extruded the 

 cystogenous material after they had been in the water for the usual 

 time. Those inside the rediae which were put in the snail juices 

 did not extrude their cystogenous material but finally died without 

 having undergone any apparent change. 



When the cercariae, after coming to the surface of the water, 

 have become attached to some substratum the contents of the 

 cystogenous glands begin to be poured out to the surface of the 

 body. While this is taking place the cercaria is in constant motion. 

 The anterior end of the body bends from side to side about the 

 posterior sucking disc as an axis. By this means the cyst-forming 

 material is moulded about the anterior end of the body as a hemi- 

 spherical mass. The posterior part of the body — behind the ventral 

 sucker — remains comparatively quiet until the tail has been broken 

 off by its lashing which becomes especially violent at this time. 

 When the tail has been broken off the posterior part of the body 

 is drawn in and takes an active part in the shaping of the cyst. 

 The opening at the narrow end of the cyst becomes closed by the 

 formation of a layer of cyst material after the tail has been cast 

 off and the posterior part of the body has begun its active twisting 

 motion. 



All of the cystogenous material is extruded within a short time, 

 so that the cyst is completely formed within five minutes from the 

 beginning of its extrusion. 



When the cystogenous cells have given off their secretion the 

 cercaria has become considerably reduced in size and now lies coiled 

 up within the cyst (Fig. 5). 8parodic movements of the cercaria 

 within the cyst may continue for a number of hours after the cyst 

 is fully formed. Usually the tail is carried away from the body by 

 its violent lashing and it may swim about for several minutes after 

 its separation from the body. 



The completed cyst is a flask-shaped structure considerably 



