1901.] SOME ARCTIC NEMEETEANS. 93 



between the circular and longitudinal layers. The last layer is not 

 very strongly developed. 



On either side of the animal, and lying partly in the longitudinal 

 muscle-layer, partly in the gelatinous connective tissue within the 

 body oi" the animal, is a well-marked layer of giand-cells (Plate VII. 

 fig. 11, gll.). This layer stretches back to the intestinal region. 

 Their secretion does not stain with borax-carmine, picric acid, or 

 nigrosin, but takes an intense pui'ple hue with thionin. The glands 

 pierce the circular muscle-layers and the basement-membrane to 

 open to the exterior. They are really the backward extensions of 

 the enormously developed head-glands, which in the snout-region 

 comprise the bulk of the tissue lying within the basement- 

 membrane. A similar arrangement is found in the genera 

 Prosadenoporus^ 2in.^ Eunemei^tes' (some species), and also in one 

 other species of Ampliiponis, viz. A. carinelloides ^. In the last- 

 named species the backward extent of these glands is not so great 

 as in A. paulinus. 



The vascular system is of the normal Amphiporid type. The 

 median dorsal vessel is formed by both branches of the head loop. 

 The vessels are small throughout. 



The blind gut does not reach nearly to the brain. Its anterior 

 limit is halfway between its point of origin and the tip of the 

 snout. 



The proboscis-sheath does not extend to the end of the body, 

 being wanting in the posterior ^th. 



The proboscis is about | of the total body length. It is found 

 coiled in the anterior 5 of the rhynchoccelom. Behind this the 

 proboscis-sheath becomes much smaller. The proboscis contains 

 1.5 nerves. Its epithelium is raised into numerous large papillae. 

 The armature consists of a central stylet and two pockets each 

 containing 4 reserve stylets. The stylet and base are of the 

 same length, viz. 130 /x. 



The excretory system commences shortly after the brain. The 

 tubules lie round the lateral nerve-cords, and are numerous and 

 fairly large (Plate VII. fig. 11, ext.). There is a single duct on 

 either side situated at the junction of the anterior 5 with the 

 rest of the system. The backward extent of the tubules is greater 

 than in A. thompsoni (Plate VII. fig. 8), and considerably greater 

 than in A. arcticus (Plate VII. fig. 9). 



The brain is fairly well developed. The ventral commissure is 

 very short and straight ; the dorsal fine and curved. The median 

 dorsal nerve is very small. The side stems form a strong supra- 

 anal commissure. 



The cerebral organs lie just in front of the brain. They are 

 small, and the greater part of their bulk consists of gland-cells. 



The head-furrows are small, not encircling more than half the 



^ Biirger, O. : " Untersuchungen iiber die Anatomie und Histologie der 

 Nemertinen, u.s.w.," Zeit. f. wiss. Zool. 1890 (p. 30). 



^ Burger, O. : Naples Monograph, The Nemertines, 1895 (p. 126). 

 ^ Burger, O. : ibid. (p. 559). 



