AFFINITIES OF ECHIURUS UNICINCTUS. 81 



where the epithelium lining the alimentary canal takes the place of the hndy integument. 

 A peculiar tissue is present within the anal spliinctor, continuing forward some distance 

 beyond the openings of the anal vesicles ; it is suggestive of l)eing the glandular 

 epidermis, modified as a result of its morphologically internal position. Its prol)al)le 

 signiticance and relations will be considered more fully in connection with the anal 

 vesicles. 



In sections of the bodj'^-wall, and more particularly in the region of the proboscis, 

 there are present in the epidermis groups of sensory cells, similar to those figured by 

 Jameson in his paper on Thalassema neptuni. Each cell possesses a projecting process 

 or hair, which, piercing the cuticle, forms a trigger-like organ (PL 7. fig. 11, c.s.) ; I was 

 unable to trace any connection between these cells and nerve-branches from the lateral 

 trunks in the proboscis. The occurrence of such structui-es as these sensory cells would 

 appear to be exceptional from what Spengel says in the account he gives of his investiga- 

 tions on S?//«o'«s Pa//«m: "Beim Echiunis habe ich weder bewegliche Cilien noeh 

 Starre Haare zu Erkennen vermocht." The only organs of a sensory nature Avhich he 

 finds are those to which he applies the term " becherformige Sinnesorgane," comparable 

 with those mentioned by Eisig * as occurring in the CapitelUdeu. In Sipunculus 

 AndresBf found between the gland-cells occasional " Nervendorgane," particularly on 

 the proboscis, but also irregularly distributed over the body. Eisig concludes that what 

 Andreae calls " Seitenorgane " are in reality the same thing as his " Beeherorgane." 



Alimentary Canal. — The alimentary canal is relatively very long, about 60 cm.; it 

 forms many coils, which are arranged for the most part quite irregularly ; yet I find 

 that some of the individual loops are constant in occurrence and disposition. In all 

 cases the mouth leads into a straight buccal cavity, which is fixed to the body-wall by 

 radial and dorsal mesenteric strands. Histologically this tract shows a ciliated glandular 

 epithelium which is thrown into folds, continuous with those on the prostomium. At 

 first the outer layer of longitudinal muscle is very inconspicuous (PI. 8. figs. 13, \Za), 

 but it gradually becomes more pronounced (PL 8. figs. 14, 14 a, m.l.). Beyond the 

 region of radial mesenteries the tube becomes narrower and takes an uninterrupted 

 backward course for about an inch ; in Ech'mrus Fallasll and Thalassema neptuni this 

 region is thrown into a double loop. As before, its lining is glandular, but the waUs 

 have become much more muscular ; at this jioint there is always a little knot of <1 to 5 

 close coils (PL 7. fig. 5, cr.), in which the muscular elements are greatly reduced and 

 the glandular nature of the epithelium is intensified, the foldings at the same time 

 becoming deeper. Prom the nature of this coiled portion I judge it to be distensible, so 

 it may function as a crop (PL 8. fig. 15). Beyond it, the alimentary canal decreases 

 still more in calibre, and runs almost straight to the posterior end of the body-cavity ; 

 its walls are immensely thick, owing to the remarkable development of circular muscle, 



* H. Eisig : " Die Seitenorgane und becherfcirmigen Orgaue tier Capitcllidcn,"' MifctheiluDgen aus der Zoolo". 

 Station zu Neapel, Bd. i. p. 278. 



t J. Andrea;: "Eeitrage zur Anatoiaie u. Histologic des Hiimnculus nadux, L.," in Zeitscli. wiss. Zool. Ed. sxxvi. 

 pp. 201-258, tabb. 12 u. lU (ISSl). 



