122 
THE VOYAGE OF H.M.S. CHALLENGER. 
colour. It is always more or less of a straw yellow, in some cases a little brighter than 
in others. 
The Ascidiozooids are always clearly visible on the surface. They are closely placed 
but have no regular arrangement (see PI. XV. fig. 14). At the upper end of the head 
they seem to be rarer than elsewhere, or absent. This part of the colony sometimes has 
a decayed appearance. The shape of the Ascidiozooids is long and narrow (PI. XV. 
fig. 17). 
The branchial sac occupies about one-half of the total length, and is considerably 
narrower than the widest part of the body, which is towards the posterior end of the 
visceral mass (PL XV. fig. 17). The vascular appendage {y.ap.) is narrow, and springs 
from the middle of the posterior end. 
The test contains a fair number of small cells scattered through the homogeneous 
matrix. Bladder cells are present in some places, but they are not very numerous. 
Some parts of the test contain very few cells indeed. The mantle is not strong. In 
some places it contains patches of large opaque white pigment cells. These are especially 
developed along the course of the endostyle towards its anterior extremity, and frequently 
form a pigmented mass which may be seen by the naked eye in a surface view of the 
colony, showing through the transparent test as a small white speck. The endostyle is 
large and conspicuous ; its course is undulating. 
The branchial sac is peculiarly long and narrow (PI. XV. fig. 17). The transverse 
vessels are wider than is usual in the genus (PI. XV. fig. 16, tr^, and have narrow 
horizontal membranes. The stigmata are large, but numerous ; they have rounded ends, 
and are bounded by very distinct ciliated cells pointed at their free ends. The tentacles 
are long and thin, and their bases are closely placed. 
The abdomen is as long as and broader than the thoracic part of the body, and is 
almost entirely formed by the alimentary canal. The oesophagus commences at the 
narrow posterior end of the branchial sac and runs backwards to open into the large 
globular stomach which forms a rounded projection upon the dorsal edge of the abdomen 
(PI. XV. fig. n , st.). The stomach is perfectly plain ; it has no ridges or folds. The 
intestine springs from the posterior end of the stomach and runs first posteriorly, then 
curves round ventrally and turning anteriorly runs forwards, and eventually crosses the 
oesophagus to become the rectum, which may be traced nearly half way up the dorsal edge 
of the branchial sac (PI. XV. fig. 17, r.). 
The reproductive organs form a rounded mass placed in the intestinal loop, and 
projecting beyond the intestine ventrally and to a slight extent posteriorly (PI. XV. 
fig. 17, t.v.). They consist in all the Ascidiozooids examined merely of spermatic vesicles, 
no ova being present. These Ascidiozooids were all large and mature, no young ones 
being found in the colony examined. The vas deferens (PI. XV. fig. 17, v.d.) leaves the 
genital gland at its posterior end and curls round ventrally and then anteriorly to reach 
