STRUCTURE OF CLINOSTOMUM 213 



stored during the period of encystment. It is thus reasonable to 

 look upon the extensive equipment of spaces possessed by the 

 excretory collecting vessel as a storage apparatus. In favor of 

 this interpretation is the further fact that in both Clinostomum 

 and the holostome just mentioned the contents of these cavities 

 begin to be discharged as soon as the worm has escaped from its 

 cyst. I think that the substances contained in the intestinal 

 caeca may also prove to be waste matters and that these cavities 

 are also being employed for storage. 



The recurrent excretory vessel. Reference has already been 

 made to a vessel which parallels the collecting vessel. It is 

 readily seen in the parts of the body behind the ventral sucker; 

 anteriorly it is lost in the maze of vessels which are derived from 

 the collecting vessel. Posteriorly (fig. 16) it bends sharply for- 

 ward, as the vessel into which the capillaries drain. This, which 

 I have called the recurrent vessel, is spirally coiled in all sections 

 and even shows this state in living animals. It is located exter- 

 nally and somewhat dorsally to the collecting vessel, but is much 

 smaller, having a diameter of only 0.02 mm. The wall is com- 

 posed of a very thin membrane. The tube is uniform in diameter 

 in all parts; unlike the collecting vessel the wall possesses no con- 

 tractility, there being no muscular tissue present. The wall of 

 this vessel is supplied at close intervals with peculiar ciliary organs. 

 In life these vibrate at a very rapid rate so that they become visible 

 only after their vitality has become lowered. Then it is seen 

 that the organ is attached posteriorly in the wall of the vessel, 

 the rest being free and pointing anteriorly so that its vibration 

 produces a current running forward in the tube. These organs 

 are located in the recurrent vessel at close intervals. Bugge 

 ('02, fig. 62) finds that in certain cercarias occurring in certain 

 helices the chief canals are supplied with 'Wimperschopfen' 

 which correspond with the organs just mentioned and in addition 

 that there is a lining of ordinary cilia clothing the rest of the inner 

 surface of the wall. There are no similar ordinary cilia in these 

 vessels of Clinostomum. The ciliary organs are many times longer 

 than the diameter of the vessel in whose lumen they lie. In 

 life I am unable to recognize individual cilia in them but in sec- 



