232 
THE VOYAGE OF H.M.S. CHALLENGER, 
colony. It is traversed in aU directions by the long narrow Ascidiozooids which run 
irregularly from the surface towards the centre. The test cells are exceedingly numerous 
and closely placed (PI. XXX. fig. 15,, t.c.), and are very diverse in shape and size. The 
opacity of the test is in all probability due to their abundance. In some places they occur 
in rounded masses in which the individual cells have become more or less polygonal from 
mutual pressure (PL XXX. fig. 15, Although the body of the Ascidiozooid is opaque, 
the mantle is not thickened, and the musculature is not very strong. The branchial 
sphincter is feebly developed. 
The branchial sac is usually much longer than it is broad (PL XXX. fig. 13), but it 
is small compared with the size of the body. In some cases the sac is about four times 
as long as it is broad, and there may be fourteen or fifteen rows of stigmata. The 
stigmata are distinct, but not large (PL XXX. fig. 14, sg.) ‘, they are closely placed and 
have well-developed ciliated cells. The endostyle is conspicuous. Its course is undulating 
(PL XXX. fig. 13, en.). 
The alimentary canal is long and narrow. It is usually of about the same length as the 
branchial sac, consequently the thorax and abdomen are nearly equal in size (PL XXX. 
fig. 13). The oesophagus is a long narrow tube ; it starts from the posterior end of the 
branchial sac, and runs directly backwards to the stomach, which is placed about the 
middle of the abdomen. The stomach is small and has a globular or a pyriform shape 
(PL XXX. fig. 13, st.). Its wall is thrown into from four to six well-marked longitudinal 
folds. The intestine is very long and is divided into several distinct regions. It leads 
backwards from the stomach as a narrow tube which runs nearly to the posterior end 
of the abdomen, and then opens into a short thick-walled pyriform cavity which bends 
ventrally and becomes continuous with a short and very narrow thin-walled tube which 
turns anteriorly and opens into the rnuch wider rectum. This la,st region may be of great 
length (PL XXX, fig. 13, r,). It runs anteriorly in a slightly undulating course alongside 
the intestine, stomach, and oesophagus, and then courses along the dorsal edge of the 
branchial sac, so as to reach the atrial part of the peribranchial cavity. Consequently 
there may be as many as four distinct regions in the intestine : — (1) the narrow piece 
stretching backwards from the stomach, (2) the short wide region, (3) the thin connecting 
tube, and (4) the long and rather wide rectum. The third portion was not distinctly 
marked in the Ascidiozooid figured (PL XXX. fig. 13). 
The post-abdomen is very long, sometimes several times as long as the rest of the 
body (PL XXX. fig. 1^, p.abd.). It contains . both male and female reproductive organs, 
and ends posteriorly in an irregularly rounded bulb. 
In some respects the external appearance of this species suggests Atopogaster elongata 
(see PL XXIV. figs. 1-3), which was found in abundance at the same locality. Station 313, 
but the Ascidiozooids are much smaller and less conspicuous in the present species, besides 
which there are many of the internal details of structure in which the two forms differ. 
