114 
THE VOYAGE OF H.M.S. CHALLENGEE. 
upper one-fourtli or so of the head is free from Ascidiozooids, being formed of test 
alone, and having a slightly decayed appearance. The peduncle of this specimen is 
regular in shape, and dijffers considerably from those of the other two specimens. It is 
narrow at the top where it joins the head. It then swells rapidly to (7 mm.) about 
twice its original thickness, and then tapers downwards, somewhat like a carrot, to a 
narrow base by which it is attached. This peduncle has a very slight yellowish tinge, 
and is marked by delicate transverse wrinkles. 
In the other two specimens (PI. XIV. fig. 1) the head is more compressed [i.e., 
the thickness is not so great as the breadth), and the Ascidiozooids seem quite irregularly 
scattered over the surface. They are in all cases more numerous near the base of the 
head than further up. The peduncle is equally thick all the way down, and has no 
yellow tinge. 
The Ascidiozooids are clearly visible in all the specimens ; they show as opaque 
whitish-grey areas about 1 mm. in diameter. In a transverse section across the middle 
of the colony the Ascidiozooids are seen to occupy a zone a little over 2 mm. in breadth, 
surroundino; a central mass of test about 3 or 4 mm. in breadth. 
The branchial region of the body is nearly of the same size as the visceral (see PI. XIV. 
fig. 5), and they are connected by a narrow neck formed of the oesophagus [ce), the 
rectum (?'.), and the vas deferens [v.d.) covered by a layer of mantle. The branchial 
aperture (6r.) is placed nearly in the centre of the wide anterior end, while the atrial 
siphon {at.) projects from the dorsal side. There are apparently no vascular appendages. 
The test is firmer even in the centre of the colony than is usual in allied species. It 
is very transparent, which is no doubt partly due to the absence of vascular appendages 
from the Ascidiozooids. The test cells are very abundant, and they are of fairly large 
size. Bladder cells are rare, and seem to be mainly if not solely in the superficial layer 
of the test. 
The mantle musculature is like that of Colella 'pedunculata. The sphincters are 
fairly strong, and there is a well-developed branchial siphon (PI. XIV. fig. 5, hr.). 
Longitudinal muscle bands radiate from the base of both apertures, and form an irregular 
network over the sides of the branchial part of the body (see PL XIV. figs. 5, 4). 
The branchial sac is nearly as wide as it is long (PI. XIV. fig. 5). The stigmata are 
large, a circumstance which gives the sac a delicate appearance. The narrow pointed ends 
of the stigmata (PI. XIV. fig. 3) form a constant characteristic. The ventral border of the 
branchial sac is very convex, and this causes the endostyle to bend almost in a C-shaped 
curve (PI. XIV. fig. 5, en.). The course of the endostyle is slightly undulating. The 
languets are shorter and stouter than usual. The tentacles are not large, and they are 
peculiarly closely placed, the line of their insertion forming a very small circle. The 
j)rebranchial zone is large, and is particularly wide at the ventral edge, where the anterior 
extremity of the endostyle is very distant from the base of the ventral tentacles. 
