NEMERTEANS 187 



represented in Z. rubescens merely by two bands of longitudinal fibers 

 (as described on p. 181), is here wanting completely. The two pro- 

 boscis nerves are conspicuous in the anterior portions, but farther back 

 spread out into a plexus as usual. The basement layer of the proboscis 

 epithelium is therefore separated from the circular muscular layer only 

 by the nerves or nervous plexus, as described on p. 181 for Z. rubescens. 

 A precisely similar condition has recently been described for Zygeu- 

 polia by Miss Thompson (I9O2), 1 and is known in other species of 

 the Lineidae. 



Cephalic glands are well developed, but extend backward only to 

 the anterior portion of the brain region. 



Cut is Glands. In the esophageal region the cutis glands form a 

 thick and distinct layer in the midst of the outer longitudinal muscles. 

 Anteriorly they lie well toward the periphery of this muscular layer, 

 but sink gradually deeper until in the nephridial region they lie in con- 

 tact with the circular muscles dorsally and ventrally. This condition 

 is retained in the intestinal region, as was described for Z. rubescens. 



Cephalic Furrows. These are deep, and broaden out dorso- 

 ventrally on their internal faces near their posterior ends. The canal 

 leading to the cerebral sense organ on each side joins the posterior, 

 broadened end of the corresponding cephalic furrow through a broad 

 papilla. 



Alimentary Canal. Mouth large, elongated, situated opposite 

 posterior ends of cephalic slits. As stated above, the esophagus is 

 seen in the living worm to be divided into two distinct regions. These 

 consist of an anterior, pear-shaped cavity (pi. xvn, fig. 4) immedi- 

 ately behind the mouth and a posterior tube, or posterior esophageal 

 chamber, connecting with the intestine. The anterior cavity is dis- 

 tinguished by its much thicker, convoluted walls and deeper color. 

 At its posterior end this chamber is widened considerably, and is then 

 abruptly constricted as it opens into the posterior esophageal chamber, 

 or stomach. This latter portion has thinner walls and paler color, and 

 likewise exhibits a constriction just before it opens into the intestine. 

 There are very marked histological differences between these two por- 

 tions of the alimentary canal, but the conditions are here so very 

 similar to those described for Z. rubesccns that the detailed descriptions 

 given on p. 182 apply equally well for the species at hand. Perfectly 

 similar conditions have recently been described for Zygeupolia and 

 other forms. 



The remarkable development of circular muscles about the posterior 



l Loc. ci/., p. 693. 



