112 
THE YOYAGE OF H.M.S. CHALLENGEK. 
middle of tlie colony only the upper ends of the appendages belonging to the Ascidio- 
zooids in that section are seen. The remainder of these appendages would appear in 
sections further down the colony in the direction of the stalk. 
The test, considering its soft and unmodified condition, is very untransparent. This 
is possibly due to the presence of the numerous opaque vascular appendages which run 
through it. Figure 4 in Plate XVI. shows the number present in a small piece of test 
from the middle of a section. The cells in the test are extremely abundant. The 
matrix, though generally homogeneous, is in some places distinctly fibrillated. Small 
spherical bladder cells are present in some places. 
The mantle musculature is very like that of Golella pedunculata. The branchial 
sphincter is fairly well developed. The atrial siphon is large and projecting (PI. XVI. 
fig. 5, at.). 
The branchial sac is rather irregular in shape. Its ventral border is always much 
contorted on account of the remarkably irregular course of the endostyle (PI. XVI. 
fig. 5, en.). Its anterior and posterior ends are wide, and usually almost straight and 
parallel to one another. The stigmata are very long, as in Colella 'pedunculata. The 
stigmatic cells are prominent and richly ciliated. The tentacles are very large, and are 
so closely placed that their bases touch (PI. XVI. fig. 7, tn.). The shorter ones are 
scarcely half the length of the larger ones. 
The alimentary canal is of fair size ; it is slightly variable in its shape and course. 
The oesophagus is always long and narrow (PI. XVI. fig. 5). It commences at the 
dorsal end of the posterior edge of the branchial sac, and runs directly or almost directly 
backwards (posteriorly) to open into the small more or less globular stomach (PI. XVI. 
figs. 5, 6, St.). The stomach usually lies about half way between the posterior end of 
the branchial sac and the posterior end of the Ascidiozooid. It has no markings 
externally, and is quite opaque. The intestine commences as a narrow tube like the 
oesophagus, and after a very short course backwards usually opens suddenly into a 
considerably wider region with thick walls (PI. XVI. fig. 6, ^.). This narrows 
slightly as it runs backwards to form the most posteriorly placed part of the intestine, 
which turns dorsally and then anteriorly to become the rectum. The rectum is long 
and very wide (PL XVI. figs. .5, 6). It runs anteriorly past the stomach and oesophagus 
and along the dorsal edge of the branchial sac, to terminate at the base of the large 
atrial siphon. It is usually filled with fsecal matter in the form of spherical dark 
coloured balls (PI. XVI. fig. .5), which are moderately firm and strong. Figure 6 
shows the alimentary canal of a younger Ascidiozooid than the one represented in 
figure 5. 
The reproductive organs are placed alongside the loop of the intestine, and a few ova 
and spermatic vesicles may frequently be seen (as in PI. XVI. fig. 5), projecting beyond 
the rectum dorsally, opposite to the stomach. 
