Life-history and Anatomy of the Appeiuliculate Distomes. 373 



walls, in which I coukl detect no definite arrangement into circular 

 and longitudinal fibres: these fibres are much more numerous in the 

 walls of the hinder and median portions of the canal than towards its 

 forward end. The excretory vesicle contains a large number of highly 

 refractive, concretionary, disk -like bodies, of round or oval shape, 

 averaging 0.0037 ram in diameter. These bodies are always more 

 plentiful in the loop of the vesicle than in its unpaired portion. They 

 are in constant motion during the life of the animal; a colorless fluid 

 seems to hold them in suspension, which, with them, is swept back 

 and forth by the contraction of the walls of the vesicle and the move- 

 ments of the animal's body. Occasionally a few of the bodies may be 

 seen to pass out of the excretory pore into the appendicular vesicle 

 or into the water. 



The structures above described form the most apparent portion 

 of the excretory system, and have been seen and described by all 

 authors under whose observation appendiculate Distomes have come. 

 They do not, however, constitute the only parts of the system, nor 

 its most important parts, physiologically. From each of the lateral 

 branches of the loop an extremely delicate, longitudinal canal passes 

 to the hinder end of the body, from which side-branches can be seen 

 to pass into the surrounding tissues (PI. 25, Fig. 2 I can). It is 

 from these side-branches that the end-tubules or capillaries undoubt- 

 edly proceed; I have been, however, unable to see these tubules or 

 the flame-cells in which they end, either in the live worm or in pre- 

 served material. 



The two longitudinal canals and their side branches could only 

 be seen in the live, compressed worm, in which they appeared as tor- 

 tuous and highly refractive lines. Even then they were only studied 

 and their course determined with the greatest difficulty, and their 

 actual union with the excretory vesicle was never positively seen. 

 They contain no concretionary bodies. These longitudinal canals have 

 not been described, so far as I can ascertain, by any previous author, 

 although JuEL (1. c.) saw portions of them and of the side-branches. 



The Digestiye System. 



This system presents few unusual features. The oral sucker is 

 a powerful organ, funnel-shaped in a state of relaxation, and with a 

 depth of 0.05 mm : when it is contracted the forward portion is tri- 

 angular in shape, not unlike the mouth of an Ascarid (PI. 26, Fig. 10). 

 At the bottom of the sucker the mouth opens into the nmscular 



