EEPOET ON THE TUNICATA. 
225 
parts of the test, near the outer surface, there are some rather larger elliptical cells 
with very granular protoplasm. 
The musculature is most strongly developed on the thorax and on the post-abdomen ; 
the abdomen has only a few delicate longitudinal bands. There are six well-marked lobes 
on the branchial siphon, and a long pointed languet is present at the atrial aperture 
(PL XXX. fig. 3, at. 1). 
The stigmata vary in size in dilferent branchial sacs. In many cases they are shorter 
and less numerous than in the piece figured (PL XXX. fig. 4, sg.). 
The alimentary canal is of relatively small size (PI. XXX. fig. 3, ahd., and fig. 6^. 
The oesophagus is a narrow tube which runs directly backwards from the posterior end of 
the branchial sac to open into the large globular stomach (PI. XXX. figs. 5, 6, st.). 
The waU of the stomach is thrown into a number of longitudinal folds, usually five on 
each side, which are clearly visible on the outer surface (PL XXX. figs. 5, Q, st.), and 
are seen in a transverse section (see PL XXX. fig. 7, st.) to be of considerable size. The 
posterior end of the stomach is slightly narrower than the anterior, and it is continued 
into the narrow intestine, which runs backwards for some distance in a slightly undulating 
course (PL XXX. fig. 6, i.). It then turns dorsally and anteriorly and passes into the 
rectum, a thin-walled tube of considerable size which runs anteriorly along the dorsal 
edge of the stomach, oesophagus, and branchial sac, and finally terminates in the peri- 
branchial cavity. The rectum has its wall folded longitudinally in two or three 
places (PL XXX. fig. 7, r.), but these folds are neither so large nor so regular as those of 
the stomach. 
The post-abdomen is large and has a small knob at its posterior end like that found in 
Atopogaster elongata (see PL XXIV. fig. 4, and PL XXX. fig. 3). The heart is placed at 
the end of the post-abdomen. The usual double membranous septum runs along the 
whole length (PL XXX. fig. 3, p.abd.), and separates two cavities in which the 
reproductive organs are situated. 
Amaroucium irregidare, var. concinnum, nov. (PL XXX. fig. 8). 
One specimen, from Station 313, differs in some respects from the other colonies 
of Amaroucium irregulare from that locality, and may consequently be recognised as a 
variety. It is of elliptical form (PL XXX. fig. 8) and is much compressed laterally. It 
is attached by a very small area at one of the ends, and measures 5 '3 cm. in length, 3'5 cm. 
in breadth, and 1 cm. in thickness. It is slightly paler in colour than most of the other 
specimens, and has almost no sand attached to the test. The most notable feature in 
it, however, is that in one region, on one of the flattened sides and especially near the 
upper end, the Ascidiozooids are arranged in distinct circular or ovate systems like those 
of a Botryllus. There are about a dozen of these systems distinctly visible and clearly 
(ZOOL. CHALL. EXP. — PART XXXVIII. — 1886.) Pp 29 
