REPOET ON THE THNICATA. 
189 
fig. 1). The common cloaca! apertures are circular, and vary from 1 mm. to 2 mm. in 
diameter. There are usually about eight Ascidiozooids in a system. On the upper 
surface of the colony the wide anterior ends of the Ascidiozooids are distinctly visible. 
They show the branchial aperture with its six lobes and the anterior extremity of the 
endostyle. On the sides of the colony the abdominal and post-abdominal regions are 
seen (PI. XXVI. fig. 1). In a body 12 mm. long the thorax is about 4 mm. in length, 
the abdomen 3 mm., and the post-abdomen 5 mm. In some cases the post-abdomen is 
relatively much longer. It extends down to the top of the peduncle. 
The test in the upper part of the colony is small in amount, as the Ascidiozooids are 
very closely placed (PI. XXVI. fig. 1). The outer surface is firmer than the inner part, 
and can be torn off as a distinct membrane. The ectoderm adheres very firmly to the 
test, and consequently it is sometimes a little difficult to separate the thoracic part of 
the Ascidiozooid from the test, and patches of the ectoderm and even small pieces 
of the mantle are occasionally left adhering to the test. The mantle is unusually 
delicate, and recalls that of some species of Colella in the Distomidse. The branchial 
aperture is distinctly six-lobed, but the sphincter is feebly developed (PI. XXVI. 
fig. 4, hr.). 
The branchial sac is usually about 4 mm. in length and 1'5 mm. in breadth. The 
number of transverse vessels is usually over twelve, and the stigmata are always well 
developed. There is a considerable amount of variability, however, in the size of the 
transverse vessels and the length of the stiganata. The characters appear to be constant 
throughout the same sac, but differ in the Ascidiozooids of one colony. Figures 2 and 
3 on Plate XXVI. show two extreme conditions. In figure 3 the transverse vessels are 
as wide as the length of the stigmata, while in figure 2 they are much narrower and the 
stigmata are larger. Each transverse vessel has a bundle of muscle fibres running along 
it (PI. XXVI. fig. 2, m.f.). The ciliated cells bounding the stigmata are always large and 
distinct. 
The dorsal languets are triangular, rather short, and flattened antero-posteriorly 
(PL XXVI. fig. 3, 1.). On account of the transparency of the mantle and branchial 
sac the endostyle is always a conspicuous object in dissections. It is unusually narrow, 
and does not undulate from side to side. 
The oesophagus (see PI. XXVI. fig. 4, oe) is long, narrow, funnel-shaped, and curved with 
the convexity dorsal. It leaves the branchial sac at the dorsal edge of the posterior end. 
The stomach is large and ovate in shape, and its long axis is directed posteriorly and 
ventrally (PL XXVI. fig. 4, st.). The oesophagus joins it by a small circular aperture on 
its inner or dorsal edge about the junction of the anterior and middle thirds. The wall 
of the stomach is not folded or thickened in any part. The intestine leaves the 
posterior end of the stomach and curves posteriorly and dorsally, narrowing until it 
reaches its most posterior point (PL XXVI. fig. 4, i.), where it enlarges to form a spindle- 
