250 COMPARATIVE ANATOMY AND PHYSIOLOGY. 



body ; the finest ducts are distributed through all 

 parts of the organism, and they pass into collecting 

 vessels, which, by the formation of anastomoses, give 

 rise to a most complicated plexus ; from these arise 



Fig. 104. Excretory System of Monoccelis fusca, showing the numerous 

 Infuudibula, and the brauchiug Tubes. (After Fraipont.) 



the efferent ducts, which gradually unite into collect- 

 ing vessels; these, again, form a plexus, and from 

 these there again arise vessels which pass into a 

 median longitudinal trunk, which opens at the hinder 

 end of the body by an excretory pore. There are 

 no valves or muscular walls by means of which the 

 products are aided on their way to the outer world. 

 The contents of the vessels are stated to be colourless, 

 and to contain a number of small particles of high 

 refractive power ; Lieberkiihn says that he has been 

 able to detect the presence of guanin. 



Among the Cestoda we find that, while the 

 young of some forms have a complicated system of 

 fine canals, the ordinary arrangement is that of two 



