44 
THE VOYAGE OF H.M.S. CHALLENGEE. 
are no larger than the fine longitudinal vessels. The stigmata are a little irregular in form 
and by no means very large. The cells bearing the cilia (PL II, fig. 5, sg. c.) are cubical 
or short columnar in form and distinctly nucleated. 
The endostyle, though narrow, is very conspicuous. Its edges are prominent, and at 
the anterior end are seen distinctly (PI. II. fig. 6) to become continuous with the peri- 
pharyngeal band. At each side of the endostyle there is a widish area (about -the size of 
a small mesh) of the branchial sac free from stigmata. 
The dorsal lamina commences anteriorly as an extremely narrow membrane which 
rapidly widens (PI. II. fig. 8, d.l). In some cases it appears to have transversely directed 
ribs or bands, but a careful examination always shows that they are merely corrugations 
or folds. The peripharyngeal band connecting the anterior ends of the endostyle and 
dorsal lamina circumscribes an oval area (PI. II. fig, 8), inside which lies the circle of 
sixteen tentacles. The four largest tentacles are placed dorsally, ventrally, and laterally. 
There is no well-marked peritubercular area, and the dorsal tubercle, which is very 
simple, appears to vary somewhat in its position, size, and shape. Figure 8 shows a case 
where the tubercle is circular, very small, and placed close to the dorsal lamina, leaving 
a wide expanse of prebranchial zone between itself and the dorsal tentacle. In the 
specimen represented by figure 9 the tubercle was somewhat ovate in form with a slight 
constriction in the middle ; it was also of larger size, and was placed about one third of the 
way from the dorsal lamina to the dorsal tentacle. In this last figure (PI. II. fig. 9) the 
specimen is represented as seen from the outer surface [i.e., from the mantle), and 
therefore the dorsal lamina is hidden by the nerve ganglion and neural gland {n.g.). The 
duct (gl.d.) leading from the dorsal tubercle to the neural gland is well seen. 
The alimentary and reproductive viscera lie alongside the posterior third or so of the 
liranchial sac (PI. II. fig. 7). The oesophagus is rather long, and is abruptly curved in 
the middle of its course. It runs at first posteriorly and dorsally and then ventrally, 
and a little posteriorly. The stomach (st) is the most posterior part of the canal. It is 
large, equally wide at both ends, and strongly ribbed longitudinally. The intestine (i) 
runs at first ventrally, then anteriorly, then dorsally, and a little ventrally towards the 
oesophagus. It then curves anteriorly to become the rectum (r), which runs anteriorly 
and terminates in a wide anal aperture, about half way down the body. The course of 
the intestine is, as a whole, transverse and parallel to the stomach, and it therefore forms 
a right angle with the rectum, which runs antero-posteriorly. 
The genital gland (g) is situated in front of the intestine, not far from the ventral 
edge. It is an irregularly lobed (PI. II. fig. 10) opaque mass. The other genital gland 
is placed on the inner face of the mantle in the corresponding position on the other side 
of the body. 
Figure 11 shows a young Ascidiozooid, many of which are found in various stages of 
development lying in the test alongside the older Ascidiozooids from which they have 
