334 
THE VOYAGE OF H.M.S. CHALLENGER. 
mantle of Goodsiria placenta, and the muscle bands are rather stronger and more 
regularly arranged (PL XLIV. fig. 7, m.). Most of them run longitudinally and trans- 
versely. The mantle is considerably pigmented ; large patches of opaque white pigment 
corpuscles occurring every here and there. 
The branchial sac is large and thin- walled, but differs from that of Goodsiria placenta 
in having the folds slight and the stigmata very small. There are three folds on each 
side of the sac, but they are very irregularly developed, being sometimes of fair size 
(PI. XLIV. fig. 6, hr.f.), while at other times they are quite rudimentary, and are repre- 
sented merely by areas where a few of the internal longitudinal bars are unusually closely 
placed (PI. XLIV. fig. 6, hr.f'.). This condition recalls what is seen in Styela grossularia 
and some other members of the Styelinse amongst Simple Ascidians. There may be from 
six to two internal longitudinal bars on a fold. There are usually three or four internal 
longitudinal bars in each interspace, in place of two as in Goodsiria placenta. Horizontal 
membranes are either absent or very slightly developed on the wide and irregular trans- 
verse vessels. The stigmata are numerous but very small (PI. XLIV. fig. 6, sg.). They 
are rather irregularly arranged, the rows being frequently inclined, and occasionally split- 
ting up into two rows or uniting again as new transverse vessels form or as two neigh- 
bouring vessels join (see PL XLIV. fig. 6). The ciliated cells are rather small, and their 
free ends do not project. There are a few muscle fibres developed in the vessels of the 
branchial sac, chiefly in the transverse vessels. 
The endostyle is large and conspicuous. Its course is straight. The dorsal lamina 
has a plain edge, and the ribs are not so distinctly marked as in Goodsiria placenta. 
The alimentary canal is fairly large. The oesophagus is short but wide ; it curves 
posteriorly and then ventrally to enter the stomach. The stomach is nearly globular in 
shape. It is directed dorso-ventrally. Its wall is thick and is thrown into a large 
number of longitudinal folds. There are usually about twenty well-marked folds ; they 
are strongly developed about the middle of the stomach and die away towards the 
oesophageal and intestinal ends. The intestine leaves the ventral end of the stomach, and 
almost at once turns anteriorly and then dorsally. It curves round the anterior edge of 
the stomach, forming rather a narrow loop, and then, opposite the oesophagus, it turns 
sharply forwards to become the rectum, which runs anteriorly for a short distance along 
the dorsal edge of the branchial sac. The intestine is rather wider than that of Goodsiria 
placenta, and the typhlosole in its interior is thrown into a series of convolutions which 
are visible through the comparatively thin walls of the intestine. The rectum is narrower 
than any other part of the alimentary canal. The system of branched tubules with 
dilated terminal bulbs is exceedingly well developed aU over the walls of the intestine, 
and it communicates with the anterior edge of the stomach by the usual duct and vesicle. 
The vesicle on the wall of the stomach where the duct opens is apparently not so well 
developed as in Goodsiria placenta. 
