04 THE VOYAGE OF H.M.S. CHALLENGER. 



portion of the sac slightly enlarged, and shows the wide, but very thin transverse 

 vessels (tr.), and internal longitudinal bars (i.l.). One of the longitudinal folds is here 

 seen (br.f.), and it shows nine internal longitudinal bars, four on each side and one at the 

 ed^e. It is obvious from the figure how the space between two adjacent bars decreases as 

 you work along the fold from tbe large mesh (ink.) of the space between the folds to the free 

 edge of the fold. PI. II. fig. 1, represents a portion of the branchial sac more magnified 

 to show the complicated branching and anastomosing of the vessels, and the way in which 

 the stigmata lie in different planes, there being in some places as many as three systems of 

 vessels crossing one behind the other. A small part is shown very highly magnified in 

 PI. II. fig. 2, to exhibit the stigmatic ciliated cells ; over the greater part of the 

 vessels of the sac the cilia have been lost. Figure 3 shows a small part of the surface of 

 a vessel still more highly magnified ; the epithelium is squamous, and the cells are large, 

 delicate, and distinctly nucleated. PI. III. fig. 4, shows a part of the branchial sac 

 where the stigmata are much more regular, the smaller vessels being; less curved. This 

 is distinctly an approach to the arrangement of the stigmata in Ascopera 'pedunculata. 



The dorsal lamina (PL III. fig. 5, and PI. I. fig. 2, d.l.), is wide, but short. There are 

 eight large and strong tentacles (PI. III. fig. 5), and the same number of much smaller 

 ones, while, alternating with these sixteen, there are about the same number of very 

 minute but still compound ones. The dorsal tubercle (PI. III. fig. 5, d.t.), is large, and 

 much coiled. There is no distinct peritubercular area. 



The oesophageal aperture (PI. I. fig. 2) is situated far forward in the branchial sac, 

 and is ear-shaped, with a double lip on the right side. It lies on a flat triangular area at 

 the posterior extremity of the dorsal lamina, at the point of convergence of the fourteen 

 branchial folds (see PI. I. fig. 2, 1-7). The oesophagus (PL I. fig. 3, oe.) is short, 

 cylindrical, and rather narrow. It runs directly posteriorly, and opens suddenly into the 

 wider end of the small pyriform stomach (st.). At the posterior narrower end of the 

 stomach the wide intestine commences. The wall of the stomach is thick, and its outer 

 surface is rough from the presence of a number of small rounded projections. This 

 structure is continued on to the first portion of the intestine, but soon dies away ; and the 

 rest of the tube has a thin membranous wall through which the coiled faecal masses are 

 distinctly seen. The wide intestine runs directly posteriorly from the stomach for a 

 considerable distance ({.), then turns round ventrally, and, after running for a short 

 distance anteriorly, turns at right angles dorsally, so as to come in contact with the first 

 part of the intestine. Here the tube, which may now be called the rectum (/•.), becomes 

 very narrow, and during the remainder of its course lies in close contact with the first 

 part of the intestine, the stomach, and finally the oesophagus. 



Along the ventral edge of the rectum lies the large, yellow, sausage-like, genital 

 gland (PL I. fig. 3, g.) with its axis directed antero-posteriorly. The duct is of moderate 

 length (g.d.) and projects from the anterior end, opening into the peribranchial cavity, 



