108 
THE VOYAGE OE H.M.S. CHALLENGER. 
groups, cause the irregular appearance of darker red spots in the axial portion. Through- 
out all parts of the peduncle (PL XV. fig. 11) the ordinary minute test cells are found 
in the otherwise homogeneous matrix. A few thin- walled vessels (PI. XV. fig. 11, v.ap.) 
are also to be seen in both transverse and longitudinal sections. They traverse the 
peduncle in its length (PI. XV. fig. 9, v. ap.), and seem to give off no lateral 
branches. 
The Ascidiozooids are decidedly small (PI. XV. fig. 7 ). The visceral mass is a little 
larger than the branchial part of the body. The vascular appendage is delicate, and 
springs from the middle of the posterior end of the body. It is clearly divided into two 
tubes running side by side. The anterior end of the Ascidiozooid is not large. It 
bears the short wide branchial siphon. The dorsal edge of .the branchial part of the 
body is more convex than the ventral. 
The test in the head is very soft. As the Ascidiozooids and embryos are very 
numerous, the test is greatly broken up. There is no large central part of the colony 
formed of test alone. Bladder cells are abundant, but they are nearly always spherical, 
not being so numerous as to be compressed into polygonal forms. The ordinary small 
cells of the test are abundant and of all shapes. The vascular appendages, which are 
found every here and there in the test, are thin and delicate. They are usually fil led 
with blood-corpuscles. 
The musculature of the mantle is very fine. In addition to the regular transverse 
bands there are some bundles of fibres crossing the others irregularly. There is a good 
deal of white pigmentation in the mantle. In addition to the patch at the anterior 
extremity of the endostyle there are sometimes clumps of cells scattered over the 
branchial region, and almost invariably there are large areas of the stomach (PL XV. 
fig. 7 , St.) and intestine which have a granular opaque white appearance from the presence 
of numerous pigment cells. 
The branchial sac is nearly as broad as it is long. There are usually four or five 
rows of stigmata on each side. The transverse vessels (PL XV. fig. 3, tr.) are 
moderately wide ; they have delicate horizontal membranes attached to their inner 
edges. The sac shown in figure 5 was probably not from a mature Ascidiozooid. The 
stigmata are relatively short and rounded, and all the parts are small. Figure 3 shows 
the shape of the stigmata in a fully developed condition. The stigmatic cells are very 
conspicuous under a high power. They are short, and their free ends project usually in 
a somewhat triangular form (see PL XV. fig. 4). The cilia are abundant. 
The dorsal languets are rather blunt at their ends. They have more of a triangular 
form when seen from above or below than from the side as in figure 5. A strongish band 
of muscle fibres may be traced along the dorsal line of the branchial sac outside the base 
of the languets (PL XV. fig. 5,d.L). The tentacles are long and thin. In several of 
the Ascidiozooids they were found projecting through the mouth of the branchial siphon 
