REPORT THE TUNICATA. 
97 
at one end around the nucleus, leaving a larger or smaller clear space between it and the 
cell-wall at the other extremity. 
The peduncle is mainly composed of investing mass, and is seen on section to be very 
spongy in texture (PJ. XIII. figs. 1-4). Large and rather irregular longitudinal canals 
traverse it in great numbers and throughout almost its entire thickness. These are 
united by a vast number of smaller vessels which run in horizontal or transverse planes 
and communicate freely with the larger vessels (PI. XIII. fig. 2, v.). The latter contain 
the vascular appendages closely attached to their walls throughout, and giving off lateral 
branches which occupy the smaller canals. Thus a colonial system of blood-vessels is 
formed, the vascular systems of the different Ascidiozooids being placed in direct com- 
munication with one another through the vascular appendages and their lateral branches 
in the peduncle. 
In a transverse section (PI. XIII. fig. l) the matrix is seen in the form of a series of 
islands surrounded by the small horizontal vessels, while here and there (PI. XIII. fig. 3) 
the cut ends of the larger vertical vessels are seen. The investing mass, as in the upper 
part of the colony, contains no bladder cells, only the small spherical, fusiform, and 
branched test cells being present (PI. XIII. fig. 4). 
Mantle . — Under this head, as in the last species, the shape of an adult Ascidiozooid 
dissected out from the investing mass will be described first. The body may be divided 
into two parts, the thorax and the abdomen, the latter of which bears the long vascular 
appendage. The incubatory jdoucIi in this species is so rudimentary as not to require 
consideration apart from the peribranchial cavity of which it is merely a portion. The 
thorax is flattened laterally and has an oblong shape (PI. X. fig. 9), somewhat narrowing 
as it recedes from the wide olfiiquely truncated anterior end wliere the two apertures 
are placed. The abdomen is rather long and narrow, and is rounded posteriorly where 
the vascular appendage projects from it (PI. X. figs. 9, 10). It is of a dark indigo-blue 
colour, and gives the deeper part of the colony in which it lies the well-marked charac- 
teristic tint. These regions of tlie body contain the same organs as in the last species. 
The mantle covers the thorax, abdomen, and vascular appendage in the form of a 
delicate sac with two openings, the branchial and atrial siphons. In its structure and 
the distriljution of the musculature it resembles the last species closely. In the thorax, 
however, the transverse parallel muscle bands are more regular and more frequent, while 
the longitudinal bands are fewer in number, and in the case of some of the Ascidiozooids 
almost entirely aljsent (PI. X. fig. 10). 
The connective tissue elements present no notable peculiarity ; a few fusiform and 
stellate corpuscles are scattered in the homogeneous transparent membrane connecting 
and surrounding the muscle fibres. The mantle is lined on its inner aspect with 
the usual layer of squamous epithelium, which is often distinctly visible in this species 
without any staining (PI. XL fig. 4). The ectoderm on the outer surface is in its 
(ZOOL. CHALL, EXP. — PART XXXVIII. — 1885.) Pp 1 3 
