168 
THE VOYAGE OF H.M.S. CHALLENGEK. 
peribrancliial cavity communicates directly with the common cloacal cavity through the 
atrial aperture, it is easy to understand how the Copepod might pass its ova into the 
peribranchial cavities of adjoining Ascidiozooids and use them as incubatory pouches. In 
one or two cases the larval Ascidians and the larval Crustaceans were found developing 
side by side in the same peribranchial cavity. 
Atopogasier aurantiaca, n. sp. (PI. XXIII. figs. 7-13). 
The Colony is irregularly wedge-shaped, with the larger end uppermost. The point 
of attachment, which is placed at the posterior end, is comparatively small, and the colony 
increases rapidly in size towards the top, which is very large and irregularly convex. The 
posterior two-thirds of the colony forms a short and very stout peduncle. The colour is 
orange, having in some places a greyish tint and in other places becoming reddish-brown. 
The surface is uneven but smooth. 
The length is about 7 cm., the greatest breadth is 6 '5 cm., and the greatest thick- 
ness 4 ’5 cm. 
The Ascidiozooids are very long (up to about 3 cm. in antero-posterior extent, and 
about 2 ’5 mm. at the widest point). The body is divided into three regions, of which 
the abdomen or intestinal part is very much the largest, being more than twice as long as 
the other two regions together. The Ascidiozooids are placed more or less vertically in 
the colony, with their anterior ends on the large upper surface ; there is no arrangement 
in systems, and no common cloacal apertures are present. 
The Test is firm and cartilaginous all over, but is particularly hard in the lower part of 
the colony. It is semi-transparent and is of a yellowish or orange-grey colour throughout. 
It is darker towards the posterior end and lighter on the upper surface. The matrix of 
the test contains many small cells of various shapes, in some places closely crowded 
together. There are very few vessels and bladder cells in the test. 
The Mantle is moderately thick, and is nearly equally muscular all over the anterior 
half of the body. The muscle bands are fine but very numerous, and they nearly all run 
longitudinally. The sphincters are well developed, and both apertures are deeply 
six-lobed. 
The Branchial Sac is of moderate size and has many stigmata placed in about twenty 
regular rows. The transverse vessels are aU of the same size, and bear short horizontal 
membranes which project inwards. The stigmata are all of much the same size, and are 
arranged with regularity. They are of moderate length, and the ciliated cells are large 
and pointed at their free ends. 
The Endostyle is large and conspicuous, its course is very undulating. 
The Dorsal Lamina is formed of a large number of long narrow pointed languets. 
The Tentacles are large and fairly numerous ; they are not all of one length. 
