68 
THE VOYAGE OF H.M.S. CHALLENGER. 
to each Ascidiozooid in the system. The edges of the lobes are somewhat A^ariegated, 
as they contain irregular patches of white and brown pigment. 
In a section of the colony it is seen that the Ascidiozooids occupy merely a thin 
surface layer 1’5 mm. to 2 mm. in thickness, while all the rest of the colony is made up 
of the soft gelatinous grey test, like the part exposed at the base of the colony, but more 
transparent. The superficial layer of test all over the colony is modified into a thin 
transparent but firm membrane ; when this is removed the underlying test is found to 
be very much softer. The vessels of the test in this species are decidedly narrow (see 
PI. IV. fig. 8, V.), and sometimes very fine vessels may be traced for a long distance. 
The terminal knobs are large, and are always more or less globular in shape. Although 
the matrix is as a general rule homogeneous, still in some parts a delicate fibrillation can 
be made out. The stellate test cells are usually very distinct. 
The mantle at first sight seems to have no musculature, but under a high magnifica- 
tion (300 diameters and upwards) very delicate fibres are found in some parts of it. 
These are decidedly finer than in most of the Botryllidse, and very much finer than those 
in the mantle of Polycyclus lamarcki. The connectives between the branchial sac and 
the mantle are very thin, and are sometimes of considerable length. 
The branchial sac is wider than usual (see PI. IV. fig. 7), and the meshes are con- 
siderably larger than in any of the other Botryllidse in the collection ; they are wider 
than long, and have usually five or six stigmata each (PI. IV. fig. 9). The usual arrange- 
ment is as follows, going along the side of the sac from the dorsal lamina to the 
endostyle : — first a dorsal series of eight stigmata, then the first or dorsal internal 
longitudinal bar, then a mesh containing five stigmata, then the second bar, then a mesh 
with six stigmata and the third or ventral bar, then finally a ventral row of nine stigmata 
bounded by the endostyle.^ The transverse vessels in some cases vary a little in size, but 
there is no regular arrangement; they have slight horizontal membranes attached to their 
inner edges ; they have usually a few delicate muscle fibres. 
The endostyle is broad (PL IV. figs. 7, 10, en.). The dorsal lamina is very distinctly 
ciliated along its free margin. Its narrow anterior end has a curious undulating course 
(PI. IV. fig. 10, d.l.). There is a certain amount of irregularity in regard to the eight 
smaller tentacles. They are always very short (PI. IV. fig. 10), but in some cases they 
are reduced to mere stumps, and some of them may be absent altogether. The pre- 
branchial zone is pear-shaped (PI. IV. fig. 10, z.), and has the narrower end ventral as in 
Polycyclus lamarcki. Two rounded masses of yellowish-green pigment are found at the 
sides of the prebranchial zone, one immediately posterior to each median lateral tentacle 
(PI. IV. fig. 10, ing.). These are the two opaque spots seen in the surface view of the 
colony (see above, p. 67). Similar cellular masses are found in the same position in 
Pyrosoma. 
' This may he expressed shortly by the following formula : — D.L. — 8 sg. — I. — 5 sg. — II. — 6 sg. — III. — 9 sg. — En. 
