REPORT ON THE TUNIC ATA. 
263 
extent (PL XXXIY. fig. 3,p.c.). They tend also to become arranged in rows end to end, 
which gives them a fibrous appearance. They are always brown, and are coarsely 
granular in texture. 
The spicules are stellate and very regular, their rays are tapering and sharp pointed 
(PI. XXXIV. fig. 4). A few spherical forms occur. The spicules never reach quite to 
the external surface, but are separated from it by a layer of test containing bladder cells 
and pigment cells. Compared with the size of the test the number of spicules present 
is remarkably small. 
The musculature of the mantle is almost entirely longitudinal in direction. A 
number of rather delicate bands spring from the base of the branchial siphon and spread 
posteriorly over the thorax. They occasionally give off branches, which unite with 
neighbouring bands, but nothing like a close network is formed. On the whole 
these bands run parallel with one another. A few transverse and irregularly running 
muscles are also present. The branchial siphon is long but narrow (PI. XXXIV. 
fig. 2). It is lined by a layer of very dark coloured test, which becomes thickened 
at the posterior end of the siphon immediately in front of the tentacles. The branchial 
sphincter is powerful. The aperture is distinctly six-lobed. 
The stigmata in the branchial sac are numerous (PI. XXXIV. fig. 2), and their 
ciliated cells are very distinct. The muscle bands running along the transverse vessels 
are strong (PI. XXXIV. fig. The endostyle is remarkably wide (PI. XXXIV. 
fig. 2, en.). Its extremities form thickened projections at the anterior and posterior ends 
of the branchial sac. The nerve-ganglion is spherical. It is situated at the base of the 
branchial siphon. 
The alimentary canal extends for a considerable distance behind- the branchial sac. 
The oesophagus is very long and narrow (PI. XXXIV. fig. 2, ce.). Its wall is usually 
thrown into a series of corrugations or slight transverse folds. The stomach is large and 
thick walled. It is usually ellipsoidal or nearly quadrate in shape, in some cases it is 
pyriform, the posterior end being narrower than the anterior. Its wall shows no folds 
or irregular thickenings. The oesophagus and the intestine where they join the stomach 
are seen in longitudinal sections to project for a short distance into its interior so as to 
form valvular arrangements (PL XXXIV. fig. 2,st.). The intestine is long; it extends 
for a short distance behind the stomach, and then turns anteriorly so as to form a narrow 
loop. The rectum runs close alongside the oesophagus in the long narrow region of the 
body which unites the thorax and abdomen (PL XXXIV. fig. 2, r.). It then runs along 
the dorsal edge of the branchial sac, and terminates in a small anus placed about half- 
way down the peribranchial cavity. 
The testis is large and of ellipsoidal form. The long conspicuous vas deferens com- 
mences by coiling spirally four or five times around the testis (PL XXXIV. fig. 2,v.d.). 
A few ova of various sizes were found in some of the smaller Ascidiozooids. Probably 
