296 DR J. STEPHENSON ON 
character, being longer and separated by a smaller angle than elsewhere. In the eleventh 
segment the ventral setee are absent, their position being occupied by the male 
aperture. 
The body-wall (figs. 10, 11) consists of the usual layers. In addition to the circular 
and longitudinal muscular layers, there is regularly present a well-marked muscular 
band, passing vertically through the body-cavity, between the dorsal and ventral setal 
sacs of the same side in each segment (fig. 10). The peritoneal cells lining the inner 
surface of the body-wall have a distinctive character (figs. 10, 11); they are fairly large, 
ovoid, and transparent ; in sections they are very slightly coloured, the only part of the 
cell-body which takes up the stain being a quantity of contained granular matter; — 
the circular or oval nucleus, with a well-marked nucleolus, is conspicuous ; they resemble — 
chloragogen cells, but are without the numerous yellow particles which characterise these — 
latter. Similar but larger cells, pyriform in shape, attached by their stalk-like narrow | 
ends, are also found on septa $ and 4, and round the nephridia of segments vu and vii. 
There is a lateral line (fig. 10), similar to that described for Branchiura sowerbyi 
(see p. 289); the cells composing it extend peripherally outwards as far as the circular — 
muscular coat, and divide the longitudinal layer along a line which runs midway between 
dorsal and ventral setal bundles; in this worm, however, the lateral line is well marked 
only in the anterior segments. No free celomic corpuscles were seen, except a few — 
yellow granular cells, which were probably detached chloragogen cells. | 
Alimentary canal.—The pharynx extends backwards through the third segment; 
its tall columnar epithelium, as also that of the cesophagus, is ciliated. From the third 
to the seventh segment the ventral wall of the canal is raised into a prominent longi-— 
tudinal ridge, due to the greater height of the epithelium along this tract (fig. 11); the 
lumen is thus crescentic. Chloragogen cells begin in segment v. 
As appendages of the alimentary canal may be mentioned paired masses of cells in 
segments vi and vil. ‘These are situated in the anterior part of the segment, ventro- 
laterally to the cesophagus ; in transverse section they have a pyriform shape, with the 
small end below, near the ventral vessel, and the glands of the same pair may unite 
with each other round the vessel (fig. 11). Some of the cells contain yellow granules 
like those of the chloragogen cells, but their general character is very different from 
that of these latter, inasmuch as they are more compact, more irregular in size and. 
shape, and stain more deeply in both cell-body and nucleus; moreover, though they are: 
in contact with the chloragogen cells, they do not merge into them, and the masses 
have a distinct outline of their own. Similar but smaller aggregations were also found 
in segments v and viii. 
The circulatory system (figs. 12, 18, 14) is of considerable interest. The dorsal 
vessel is ventral in position for the greater part of its course; it runs alongside and on 
the left of the ventral vessel ; both are sinuous, the ventral vessel more markedly so; the 
convexities of their curves face away from each other. The dorsal vessel is somewha 
laterally situated in segments xi and x; it becomes more ventral again in ix, only to— 
