KEPOET ON THE THNICATA. 
265 
layer of test is merely a superficial layer or crust, in most places about 1 mm. in thickness. 
The remainder of the test forms a semi-transparent hyaline mass. Sections of the deeper 
part of the test show comparatively few spicules (see PI. XXXIII. fig. 4), while the test 
cells are abundant, of large size, and vary greatly in shape. Some of them are stellate 
and have their angles prolonged into processes which connect them with the angles of 
adjacent cells. Vascular appendages containing muscle fibres are found running 
vertically through the deeper parts of the test ; they form more or less parallel lines (see 
PI. XXX III. fig. 4, v.ap.). 
The Ascidiozooids are short, and are more or less rounded in form. Their branchial 
apertures, when examined from the interior, are found to be small and rather variable in 
shape. Usually they are rounded or irregularly hexagonal, but they may be stellate 
(probably the result of contraction), and in the example figured (PL XXXIII. fig. 5) the 
aperture is distinctly triradiate, its margin having three well-marked lobes. The 
sphiucter muscle [sph.) surrounding the branchial aperture is strong, and from its outer 
edge a number of radiating bands arise and run posteriorly over the body, forming the 
longitudinal muscles of the mantle. 
The test immediately around the branchial aperture is in some cases free from spicules 
(PI. XXXIII. fig. 5), and consequently forms a circular lighter-coloured area representing 
the anterior end of the Ascidiozooid ; but in other specimens the spicules extend up to 
the edges of the aperture (PI. XXXIII. fig. 3, sp.). The commonest form of spicule 
in the test is seen highly magnified at Plate XXXIII. figure 6, a. Spicules with narrower 
and more sharply pointed rays are also found, and more rarely spherical forms with 
short blunt projections occur (see PL XXXIII. fig. 6). 
The ahmentary canal forms a short open loop. The stomach is small and of rounded 
form. The testis is very large, and the vas deferens form a number of close spiral coils 
around it (PL XXXIII. fig. 7). 
A number of fully-developed tailed larvae were found imbedded in the common test. 
They are of very large size, usually larger than the Ascidiozooids, and have two distinct 
pigmented sense organs (see PL XXXIII. fig. 8). 
Didemnum(J) inerme, n. sp. (PL XXXIV. figs. 6, 7). 
The Colony is a rounded mass attached by the greater part of its lower half. The 
upper surface is convex and quite smooth. The colour is a dull grey. 
The length is 1’2 cm., the greatest breadth is U5 cm., and the greatest thickness is 
1'3 cm. 
The Ascidiozooids are apparently small and not very numerous. They are scattered 
irregularly in the upper layer of the colony, and seem not to be arranged in definite 
systems. No common cloacal apertures are visible. 
(ZOOL. CHALL. EXP. — PAKT XXXVIII. — 1886.) 
Pp 34 
