ZooL— Vol. III.] HEATH— EPIDELLA SQUAMULA. 125 



On either side of each lateral canal several branches arise 

 which extend to all the organs in the posterior half of the 

 animal. Owing to the innumerable yolk-glands only the 

 larger branches may be seen, and it consequently becomes 

 impossible to determine whether they form an anastomosing 

 system. One large canal situated immediately behind the 

 ovary is in some cases, at least, a commissural vessel con- 

 necting the two lateral canals, and also giving rise to several 

 small branches which extend into the surrounding tissues. 

 Posteriorly the lateral vessels approach each other, and 

 pass into the pedicel side by side. From sections they ap- 

 pear to unite upon their entry into the disc, though of this 

 I am not certain. From extended observation it seems 

 positive that a terminal contractile reservoir does not exist 

 in this region, nor was any trace whatever found of a 

 median exterior communication. While the main branches 

 and many of the smaller twigs may readily be distinguished 

 in the body proper, no definite trace of them exists in the 

 posterior sucker ; and in vain also were terminal cells looked 

 for in the latter. Often after transferring specimens into 

 the clearing agent many delicate canals in the disc have 

 been found, filled with air, but in every case these coincided 

 exactly with some of the larger nerve fibers. Various au- 

 thors have called attention to the fact that the nerve cords 

 of some of the trematodes appear to traverse a spongy sub- 

 s.ance which shrinks after treatment with reagents. It 

 accordingly becomes a difficult task to determine whether 

 the above described canals are branches of the excretory 

 system or an artificial product. 



As already indicated, the contents of these vessels con- 

 sists of a transparent fluid containing relatively few refrac- 

 tive granules. In the vicinity of each flame-cell this is 

 driven along by the vibrating cilium, but in the larger vessels 

 irregular peristaltic movements may be seen occasionally. 

 In some cases this appears to be due to the general move- 

 ments of the body, but at other times it becomes so definite 

 that they seem to be caused by special muscles, though 

 I have never been able to demonstrate their presence. 



'^' May 23, 1902. 



