The Microscope. 37 



The tortuous segmental organs are a single pair in each segment 

 except the oral, and perhaps the anal. They open externally by a 

 minute pore near the centre of the ventral surface, and close to the 

 median line of the body. The tubules are intimately adherent to 

 each other, forming a flattened cluster, one margin of which is usu- 

 ally attached to the body wall, the rest of the organ floating freely 

 within the body cavity. A long duct connects each with the side 

 of the intestinal canal, and opens by an external orifice as already 

 indicated. The tubules do not originate by a dilated, funnel-like 

 orifice, but by a slightly expanded opening whose aperture, and the 

 external walls for a short distance, are clothed with long, fine cilia 

 (Fig. 2). 



Mr. E. C. Bousfield {Journal Linncean Society of London, xx, 

 1887) " regards the segmental organ as purely mechanical in func- 

 tion, ' in preventing undue distention of the body by the fluid which 

 passes through the walls of the intestine, and is doubtless charged 

 with effete material from the blood-vessels which run in contact with 

 it' Moreover, what is generally considered to be the movement of 

 cilia in these organs he maintains to be due to the vibration of a 

 membrane, the free edge of which can be seen when vitality is at a 

 low ebb. Observations on Tiibifex, Hais, Stylaria, and ^olosoma 

 lead him to this view."* That the vibratory appearance within the 

 tubules is due to an undulating membrane is not correct so far as the 

 present species of JEolosoma is concerned. Not only are the inter- 

 nal walls ciliated, but the cilia project beyond and around the free 

 extremity and, in some instances, extend for a short distance doAvn 

 the external siu-face. 



The dorsal vessel, at its anterior portion contracts vigorously. 

 Near the posterior region of the digestive enlargement of the alimen- 

 tary canal it divides into several ramifications which extend over the 

 surface of the part, and presumably reunite anteriorly to form the 

 single vessel there conspicuously visible. At the posterior border of 

 the pharynx the dorsal vessel gives off two lateral branches which 

 extend around and below the pharyngeal passage, and unite to form 

 the single ventral vessel, while the main trunk continues forward to 

 beyond the mouth wherfe it furcates into a right and left hand 

 branch, each of which passes downward and backward to join the 

 ventral portions of the pharyngeal vessels . This is at least my 

 interpretation of the appearances. As the blood is so nearly color- 

 less, and the dorsal vessel is clearly visible only during its expan- 



* Jour. Royal Micros. Soc, October, 18S7. 



