332 
THE VOYAGE OF H.M.S. CHALLENGER. 
stretching from the base of the branchial tentacles more than half-way to the base 
of the atrial siphon (PL XLIII. fig. 10, n.g.). The peripharyngeal band is regular. It 
forms a slight peritubercular area on the dorsal edge. 
The layer of test lining the atrial siphon is thrown into a series of corrugated ridges, 
about twelve in number, and leading downwards from the edge of the obscurely four- 
lobed aperture to the circle of atrial tentacles (PI. XLIII. fig. 10, at.). 
The oesophageal aperture is placed far back on the dorsal edge of the branchial sac. 
The oesophagus is a short curved tube which turns ventrally and leads into the narrow 
dorsal edge of the stomach (PI. XLIII. fig. 6, cb, st.). The long axis of the stomach 
lies dorso-ventrally. On its anterior wall, near the intestinal end, there is a short caecum 
(PL XLIII. fig. 8, ves.) which receives two ducts, one coming from each side of the 
intestine, where they branch into a large number of delicate tubules. The intestine on 
leaving the ventral edge of the stomach runs ventrally for a short distance and then 
turns anteriorly and dorsally in a wide curve. It runs parallel to the stomach and 
oesophagus till it reaches the dorsal edge of the body, and then turns sharply forwards 
to become the rectum (PL XLIII. fig. 6, r.), which runs for a short distance anteriorly 
along the dorsal edge of the branchial sac and ends in an anus with a slightly thickened 
border (PL XLIII. fig. 6, a.). Figure 5 represents on a smaller scale the alimentary 
canal of an Ascidiozooid where the axis of the stomach and of the middle portion of the 
intestine were not dorso-ventral in direction (their usual condition), but were inclined 
ventrally and posteriorly (compare figs. 5 and 6 on PL XLIII.). 
The longitudinal folds on the stomach are regular and closely placed. They are from 
fifteen to twenty in number. A typhlosole is present in the intestine. The system of 
glandular tubules on the intestine is well developed (PL XLIII. figs. 7, 8, h.t.), and 
extends up the rectum to the anus. The tubules branch freely, and their ends form 
ovate dilated bulbs. They join to form a large duct on each side of the middle portion 
of the intestine, and these ducts open into the rounded projection on the anterior edge 
of the stomach (PL XLIII. fig. 8, ves.). The posterior edge of the stomach-wall is con- 
nected with the mantle externally by a large blood-vessel (PL XLIII. fig. 6). 
The reproductive organs are imbedded in the mantle (PL XLIV. figs. 4, 8, 9), and 
form thickenings projecting into the peribranchial cavity, which may be compared with 
the polycarps of the genus Polycarpa amongst Simple Ascidians. Some of the polycarps 
are much more convex than others (compare figs. 8 and 9 on PL XLIV.). 
The ova are few in number, and are generally placed near the centre of the polycarp 
(PL XLIV. fig. 8, o). The oviduct is a very wide slit, which usually appears curved in a 
crescentic manner in sections (PL XLIV. fig. 8, o.d.). 
The spermatic vesicles are numerous, and are placed on all sides of the ovary 
(PL XLIV. fig. 8). They are pyriform vesicles (PL XLIV. fig. 10, t.v.) with delicate 
ducts, which join in twos and threes to form larger tubes which finally unite into one 
