274 F. 31. Tarnhull— Anatomy and Habits of Nereis virens. 



In some of the large worms the denticles are as small as those of 

 smaller worms, while in other cases they are much larger. The large 

 denticles probahly are knocked off in some way and new ones grow 

 in their place. This would account in part for the large number of 

 very small denticles, and also for the variations in number. 



Attached to the anterior end of the oesophagus, one on each side, 

 are two salivary glands (figs. IH and 20, j). These are free except at 

 one end, and are ciliated on their outer surface. The intestine proper 

 (figs. 16 and 20, r) is straight and is constricted somewhat by the 

 muscular partitions of each segment through which it passes. It is 

 brilliant greenish yellow in color and is surrounded by a regular cap- 

 illary network of blood vessels (fig. 20). 



The internal surface of the oesophagus is tessellated with low, rounded 

 papillae or tubercles, "^rhese are regular in shape and equal in size. 

 Their sides are diag<mal to the length of the oesophagus. They show 

 through the walls of the oesophagus, so that its outside appears tessel- 

 lated with dark squares, and as the oesophagus is stretched or con- 

 tracted they become diamond shaped. The tubercles are of a dull 

 color, between brown and yellowish green. 



The intei'ior surface of the intestine is also covered with regular 

 longitudinal rows of low, rounded tubercles, which are much smaller 

 than those of the (esophagus. They are greenish-yellow like the out- 

 side of the intestine. The end of the oesophagus projects into the 

 cavity of the intestine, and its opening, which has sphincter and also 

 longitudinal muscles, can be enlarged or contracted to a considerable 

 extent. The outer surface of this end of the oesophagus is continuous 

 with and like the internal surface of the intestine. The latter secretes 

 a brown fluid in its interior and probably acts as a hepatic organ. 

 The dental portion of tlie proboscis acts like a gizzard, and the 

 oesophagus is pi'obably a sort of stomach. 



Circulation and Respiration. 



The circulatory system is highly developed and complicated. The 

 blood is red, and the vascular system is complete and closed. The 

 principal vessels have a longitudinal course, occupying the whole 

 length of the median line of the l)ody, one as a dorsal (figs. 20- 

 24, a), and the other as a ventral vessel (Ji). They are contractile, and 

 by a sort of peristaltic motion the blood is pushed forward in the 

 dorsal vessel, and in the op])osite direction by the ventral vessel. 

 The dorsal vessel is visible for nearly its whole length thi'ough the 

 more or less transparent walls of the body, and its blood can be seen 



