308 PROFESSORS EDWARD FORBES AND J. GOODSIR ON SOME 
nearly on the same level. The outer tunic is a smooth and transparent softly 
cartilaginous sac of a pale emerald green tint, slightly swelling out above the 
centre, and contracted, but not pedunculated at the base. The inner tunic is 
clearly seen through the walls of the outer; it is rather less in dimensions than 
the outer, and its shape is plainly indicated by the opaque white lines which 
mark its boundaries. ‘The orifices of the outer tunic are both quite plain; the 
branchial one is rather longer than the anal, as is also the case with the openings 
of the inner tunic. The branchial orifice of the latter is fringed with a circle of 
pointed tentacula more than twelve in number; its anal orifice is at the end of a 
short tube, and has no tentacula, but six conspicuous white ocelli. Beneath the 
branchial orifice are two crescentic white lines, at the summit of a single white 
line which runs down the branchial side of the body; under the anal orifice 
there is a short oblique central white line running from the neighbourhood of a 
large ganglion to the summit of two white lines uniting in a loop at the point 
of junction, and running down the visceral side of the body. The chief visceral 
mass is seen at the base of this line imbedded in the common pedicle. 
When the entire mass was first dredged up, many of the tests appeared as if 
emptied of their contents, or as if the inner tunic and viscera had not become 
developed. After it had for some time remained at rest in a vessel of sea-water, 
to our great surprise we found all the sacs filled up again. On closer examina- 
tion, we found that the inner tunic is exceedingly irritable, and can withdraw 
itself like the finger of a glove, entirely independent of the outer tunic, and hide 
itself in the common mass or peduncles. This is done very rapidly sometimes, 
at other times rather slowly; most rapidly when the ganglionic mass between the 
orifices is pinched or otherwise irritated. When-we squeezed it with the forceps, 
the withdrawal of the common branchial sacs was almost instantaneous. 
The genus Syntethys differs from Diazona in the structure of the branchial 
and anal orifices, which, instead of being six-rayed, as in the latter genus, are 
simple and even-edged as in Clavelina ; moreover, instead of having a peduncu- 
lated, it has a sessile abdomen. The structure and form of the common mass is 
similar, making a strong distinction between it and Clavelina. The following 
summary of the characters of Syntethys will serve to compare them with those of 
the genera described by Saviany. 
Common mass sessile, gelatinous, forming a single orbicular system. Jndivi- 
duals very prominent, arranged subconcentrically. Branchial and anal orifices 
simple, and not cut into rays. 
Thorax oblong and cylindrical. Branchial chamber with thirteen transverse 
rows of oblong openings, fringed with ciliated epithelium ; hooked fleshy tubercles 
at the intersections of the branchial meshes, each mesh presenting one of the 
ciliated openings; the tubercles give the internal surface of the chamber a dotted 
appearance. 

