158 
THE VOYAGE OF H.M.S. CHALLENGER. 
increases in size towards the top, which is large and irregularly convex. The posterior 
half or two-thirds forms a short stout peduncle. The colour varies from dark grey near 
the point of attachment to light yellowish-grey at the upper end. The surface is very 
uneven, but is smooth and glistening. 
The length is about 8 cm., the greatest breadth is 5 ‘5 cm., and the greatest thickness 
is 2*5 cm. 
The Ascidiozooids are very large (up to 2 cm. in antero-posterior extent, and about 
2*5 mm. at the widest point). The body is divided into three distinct regions; the 
thorax is about 4 mm. in length, the abdomen 3 mm., and the post-abdomen from 2 mm. 
to 14 mm. in length. The branchial and the atrial apertures are both six-lobed. The 
Ascidiozooids are placed vertically in the colony, with their anterior ends on the 
convex upper surface ; there is no arrangement in systems, and no common cloacal 
apertures are present. 
The Test is firm and cartilaginous in the lower part of the colony, but soft and 
gelatinous in the upper part. It is semi-transparent and of a grey colour throughout, 
var}fing from a dark bluish-grey at the posterior end to a light yellowish-grey on the 
upper surface. The matrix of the test is crowded with minute cells of various shapes ; 
no bladder cells or pigment cells are present. There are very few vessels in the test. 
The Mantle is strong, and has a well-developed musculature. The muscle bands on 
the branchial region are very thick, and they branch to form an irregular network. Over 
the long genital region of the body the mantle contains a number of closely placed 
longitudinally running bundles of muscle fibres. These are narrow, and do not branch. 
In the intestinal region the mantle is thin, with little or no musculature. 
The Branehial Sac is large, and contains a great number of stigmata, which vary in 
size from small round openings to very long narrow slits. The transverse vessels d iff er 
greatly in their breadth. Where they lie between rows of small stigmata they are very 
broad, but where the stigmata in the adjacent rows are long, the transverse vessels are 
considerably reduced in size. There are no horizontal membranes, but the transverse 
vessels bear rows of irregularly shaped papillse projecting into the interior of the sac, 
and usually having their free ends more or less lobed. As a rule, these papillse are 
largest where the neighbouring stigmata are small. 
The Endostyle is large and conspicuous. It has a very undulating course. 
The Dorsal Lamina is formed of a large number of closely placed languets. 
The Tentacles are numerous and of different lengths, but are not arranged with any 
regularity. 
The Dorsal Tuhercle is in the form of an ovate slit of considerable size, surrounded 
Ijy Ijroad raised margins. 
The Alimentary Canal is large, and is of an opaque greyish-yellow colour. The 
stomach is large, and its wall is longitudinally folded. The rectum is very wide. 
