NEMERTEANS l6l 



of head white, and this white color extends as a narrow band back- 

 ward along ventral median line as far as the intestinal region (pi. xvi, 



fig- 7)- 



In some individuals of the other varieties mentioned a much paler 

 band extends backward along the middle of the ventral surface in the 

 esophageal region, and this band is often directly continuous with the 

 pale color of the ventral surface of the head. In most cases this ven- 

 tral band is not sharply demarcated, but shades off gradually into the 

 darker color toward the sides of the body. 



Other specimens are pale brick red in esophageal region, and chest- 

 nut brown posteriorly, with ventral surface grayish or pale reddish. 

 In fact, there are all possible gradations between the most extreme 

 color varieties. 



Pigment to which color of body is due resides among the basal por- 

 tions of the cells in the integument. The pigment of the cephalic 

 marking, on the other hand, is situated among the cephalic tissues 

 internal to the circular muscles. When the worms are kept for some 

 time in stale sea water these outer tissues, including the pigment, are 

 sloughed off, but the worms, which are very hardy, remain alive and 

 crawl about for several hours more in this condition. Such worms 

 are pale pinkish or flesh color with the ocelli and red blood vessels 

 showing very conspicuously. 



The general brownish color on the dorsal surface of the worms is 

 retained after long preservation, and the cephalic marking is perfectly 

 distinct even after imbedding in paraffin. 



Ocelli, The four medium-sized ocelli lie deep in the tissues of the 

 head and occupy a variable position as regards the cephalic marking. 

 Their position also varies greatly according to the state of contraction 

 of anterior portion of body. When head is somewhat contracted the 

 ocelli form a square (pi. xvi, fig. 8), but when well extended (pi. xv, 

 fig. 7 and pi. xvi, fig. 6) the distance between anterior and posterior 

 pairs of ocelli is considerably greater than between the two ocelli of 

 the same pair. In an occasional specimen one or more of the ocelli 

 are double, owing, no doubt, to fragmentation of the normal ocellus. 



Size. Largest specimens found were about 70 mm. long, and 

 about 2 mm. in diameter, while the majority of sexually mature indi- 

 viduals were not more than 20-30 mm. long and i mm. wide. Many 

 immature individuals were of much smaller size. 



Proboscis. Proboscis sheath extends to posterior end of body. 

 Proboscis pale, often slightly pinkish. It is provided with ten con- 

 spicuous nerves. Basis of central stylet of the ordinary conical form, 



