' NEMERTEANS 163 



"'distance, and then unite with the main caecum, situated beneath the 

 esophagus, as usual. Other pairs of slender diverticula are given off 

 at intervals from the main caecum, and these also pass forward to the 

 dorsal side of the lateral nerves and end blindly at their anterior ends. 

 The posterior portion of the esophagus is not very slender, and it unites 

 with the intestine in front of the most anterior sexual glands. 



Blood System. The blood vessels are often very conspicuous in 

 life, especially on the ventral surface of the body, because of their deep 

 red color (pi. xvi, fig. 9). The coloring matter resides in the cor- 

 puscles themselves, which are oval and discoid. The union of the 

 three longitudinal vessels at the posterior end of body is especially con- 

 spicuous, and corpuscles are seen to pass freely, but without regularity, 

 in either direction in the same vessel. Their movement, either back- 

 ward or forward, seems wholly dependent on the contraction of par- 

 ticular parts of the body, and is not controlled by any direct contrac- 

 tion of the walls of the vessels. 



The blood vessels are also conspicuous in sections because of their 

 content of large corpuscles with deeply staining nuclei. In many cases 

 the vessels are so closely packed with these corpuscles that they are 

 more conspicuous in the stained sections than most of the other organs 

 of the body. The dorsal vessel lies within the rhynchocoel in the an- 

 terior portion of its course. The general relations of the vessels areas 

 in related species, and the presence of the corpuscles allows the course 

 of even the smaller vessels easily to be followed. Similar corpuscles 

 are found abundantly in the rhynchocoel. 



Nephridia. The nephridial tubules extend from the brain region 

 well back toward the end of the esophageal region. The tubules are 

 largest anteriorly, where they ramify in the body parenchyma both 

 above and below the lateral nerves, as well as beside, and a little in 

 front of, the brain. There is a single pair of large efferent ducts, and 

 usually one or more pairs of smaller ones. The large ducts are situ- 

 ated about on a level with the posterior ends of the dorsal ganglia, and 

 pass obliquely downwards to open somewhat below the lateral margins 

 of the head. Sometimes a second, smaller efferent duct lies near the 

 larger one. Well back in the esophageal region a pair of smaller 

 efferent ducts pass above the lateral nerves to open a little below the 

 lateral margins of the body as usual. These smaller accessory ducts 

 are not found in all individuals. 



Cerebral Sense Organs. These sense organs are situated some 

 little distance about their own diameter in front of the brain, and 

 somewhat nearer the ventral surface. The large ducts which com- 



