REPOET OlSr THE TUNICATA. 
155 
to be more numeroiTS around the edges of the head, and the centre of the upper 
surface is more or less free from them. In one specimen there is an opening in the test 
at this point which is probably a common cloacal aperture. In two of the other colonies 
there is a distinct depression in the same region, and the surface of the test has a 
contracted appearance, so it is very probable that the centre of the upper surface is 
occupied by the common cloacal aperture, and that the Ascidiozooids are arranged more 
or less irregularly around this spot. The thorax of the Ascicliozooid is longer than 
the abdomen, but not so wide (see PI. XXL fig. 5), while the post-abdomen is longer 
than the thorax and the abdomen together. 
The Ascidiozooids are of a pale opaque yellow colour, the test being grey and trans- 
parent. The test is very firm. Its siuface glistens in parts but is not very smooth. 
Here and there a few grains of sand are found adhering. The test cells are very 
numerous in some places (PI. XXL fig. 6, t.c.). The matrix, although apparently 
structureless, seems to be denser in some places than in others, and in these regions 
stains more deeply with aniline blue and picrocarmine (PI. XXL fig. 7), 
The musculature of the mantle is strong. The transverse bands are especially large 
(PI. XXL fig. 8), while the weaker longitudinal bundles are not confined to the branchial 
region but are continued cIovti to the post-abdomen. The branchial siphon is of 
considerable size, and is cylindrical in shape (PL XXL fig. 5). The sphincter occupies 
a large area. The mantle as a whole is very opaque, except over the reproductive organs 
in the post-abdomen. The muscle fibres are fusiform and not long (PI. XXL figs. 10, 11) ; 
they have large central nuclei surrounded by granular protoplasm (PI. XXL figs. 9, 10, 11). 
These simple muscle fibres are grouped in bundles in such a way that their large nuclei 
come more or less in line, and form conspicuous bands crossing the muscles transversely 
(PL XXL figs. 8, 9). 
The branchial sac is the most remarkable organ in this species. It is exceedingly 
simple (PL XXL fig. 12), and has exactly the structure which is found in some of the 
deep-sea Simple Ascidians {e.g., the genera Culeolus and Fungulus in the Bolteninae and 
Bathyoncus in the Styelinse^). 
The sac consists merely of transverse and longitudinal vessels of much the same 
calibre (see PL XXL fig. 12, tr., and i.L). The spaces between them cannot be called 
stigmata on account of their large size and their nearly square shape. Also, as in the 
correspondiog forms of branchial sac in Simple Ascidians, no cilia are present, this being 
another reason why the spaces should not be considered as stigmata. And yet if they 
are not stigmata the longitudinal vessels cannot correspond to the fine interstigmatic 
vessels of other forms, and must be regarded as internal longitudinal bars, which the 
similar vessels in Culeolus probably are, I prefer this alternative, although it 
necessitates the separation of this form from the other Polyclinidse, none of which have 
1 See Part I. of this Report (in vol. vi., 1882, pp. 90, 122, 127, and 165). 
