ALASKA NEMERTEANS 67 



tral side, pass backward for some distance on the right and left sides 

 respectively, and later spread out into a cylindrical plexus immediately 

 internal to the muscular layer, and separated from the inner epithelium 

 only by a few longitudinal muscular and connective tissue fibers. 



Glands. — The cephalic glands are very well developed, and occupy 

 a large portion of the region of the head in front of the brain, both 

 above and below the rhynchodseum. They do not extend posteriorly 

 quite so far as the brain. 



Nerves. — The nervous system is far more easily made out than in 

 any of the related species with which I am acquainted. The individ- 

 ual nerves are large and are sharply defined in all cases. The nerves 

 extending from the brain toward the tip of the snout are numerous 

 and are all of large size. The esophagal nerves are also surprisingly 

 large and quite conspicuous. They have several transverse connecting 

 branches after their origin from the ventral ganglia. The most pos- 

 terior of these connecting branches occurs just in front of the mouth. 

 In the mouth region they communicate in several instances with the 

 lateral nerves by means of branches which pass through the nervous 

 plexus outside the circular muscular layer. These branches from the 

 lateral nerves follow the nervous plexus to the vicinity of the esophagal 

 nerves, which they join by passing directly through the circular mus- 

 cular layer. I do not know that such an anastomosis between the 

 lateral nerve cords and the esophagal nerves has been previously noted 

 in any species. 



The median dorsal nerve, situated just outside the circular muscular 

 layer, is unusually conspicuous, and throughout a considerable portion of 

 the intestinal region is supplemented by a second median nerve lying 

 directly beneath the first, but in the midst of the internal longitudinal 

 muscular layer. Branches connect these two nerves at frequent inter- 

 vals. 



Cerebral sense organs. — Voluminous. The canals leading to the 

 exterior open on the summit of a broad papilla situated at the posterior, 

 widened end of each of the cephalic slits. 



Nephridia. — The nephridial canals are of much greater diameter 

 than I have observed in any other Nemertean. The canal on either 

 side is, throughout a portion of its length, equal to the lateral nerve 

 cord in cross section. The nephridia extend through the anterior half 

 of the esophagal region. The main tubule has a few very large 

 branches, and these lie in the walls of the blood spaces about the esoph- 

 agus. Anteriorly the branches lie mainly dorsal to the lateral 

 nerves, but towards the posterior ends of the nephridia the branches 



