344 
THE VOYAGE OF H.M.S, CFALLENGEB. 
The test is small in amount in this species, being reduced to thin membranes and 
narrow bars separating and surrounding the bodies of the Ascidiozooids. The upper 
layer forms a membrane, which is distinctly tougher than the part below. The test cells 
are few in number and of small size, and throughout the greater part of the test the 
vessels are few and inconspicuous. On the thin expanded margins, however, they 
become more numerous, and are usually found filled with blood-corpuscles. The long 
ovate bulbs on the terminal twigs are well marked. They resemble those found in a 
similar position in some species of Botryllus. 
The muscle bands in the mantle run transversely and longitudinally (PI. XLVI. 
fig. 12), but they are delicate. 
The branchial sac is very like that of some Styelinse amongst Simple Ascidians. The 
narrow transverse vessels crossing the meshes are well marked and are normally three in 
number (PI. XLVI. fig. 10, tr'.), but in many of the meshes one and sometimes two of 
them are absent. The meshes are usually square and of large size, but along certain 
tracts, especially on each side of the dorsal lamina, three or four of the internal longi- 
tudinal bars become more closely placed (see PI. XLVI. fig. 1 0) so as to form rudimentary 
folds, such as are seen in the branchial sac of Styela grossularia and some allied forms. 
The larger transverse vessels are variable in calibre (PI, XLVI. fig. 10, tr.). In some 
sacs they are much narrower than is shown in the figure. The internal longitudinal 
bars of the branchial sac are rather wide (PI. XLVI. fig. 10, i.l.). A single row of very 
large meshes, containing each about twelve stigmata, lies between the dorsal^ lamina and 
the rudimentary fold. Both the endostyle and the dorsal lamina are narrow. 
The stomach is pyriform and of considerable size. About eight longitudinal folds are 
visible upon its side. It tapers gradually into the intestine, which turns anteriorly and 
then dorsally and runs alongside the anterior edge of the stomach so as to form a very 
narrow intestinal loop. The shape and course of the alimentary canal resemble some- 
what those of Botrylloides tyreum^ (see PL II. fig. 7). The system of glandular tubules 
with dilated ends is well developed, and covers the greater part of the intestinal wall. 
The polycarps are fairly numerous (PI. XLVI. fig, 12) ; they are not imbedded in 
the mantle, but project freely into the peribranchial cavity in the form of ovate or 
pyriform bodies, with narrow bases or short stalks by which they are attached to the 
mantle, and long tubular projections upon which their ducts open (see PI. XLVI. fig. 12). 
The male poly carps are usually smaller, and are more of an irregularly rounded form, 
with no visible projections, or only very short ones (PI. XLVI. fig. 13). In the female 
polycarps the more mature ova occupy the upper part of the structure, while very young 
ova are found at the lower end, next to the stalk (PL XLVI, fig. 12). Female polycarps 
in various stages of development were noticed. They commence as one (PL XLVI, 
fig. 1 2, upper end) and then two or throe young ova which are imbedded in the mantle, 
1 Named Botrylloides purpureum on plate. 
