196 
THE VOYAGE OF H.M.S. CHALLENGER. 
The post-abdomen is swollen in its upper part where the reproductive organs are 
placed, and is very narrow in its lower part (PI. XXV. fig. 9, p.ah.). The edges are much 
corrugated. The ova are large and opaque. The vas deferens is wide and conspicuous in 
its whole course (PI. XXY. fig. 9, v.d.). At the posterior extremity of the post-abdomen 
there are one or two short ceecal projections, resembling rudimentary vascular append- 
ages (PL XXV. fig. 9, v.ap.). 
Fully developed tailed larvae were found in the peribranchial cavities of several of 
the Ascidiozooids. The body of the larva is narrow and elongated. There is a single 
pigmented sense-organ placed rather far back. 
Polyclinum incertum, n. sp. (PI. XXVI. fig. 10). 
The Colony is a small irregularly rounded mass attached by one end and sometimes 
slightly pedunculated. The upper surface is broad and convex. The colour is a dark 
grey with a slight brownish tinge. The surface is uneven and not smooth. 
The length is P3 cm., the breadth 1‘2 cm., and the thickness 1 cm. 
The Ascidiozooids are long and narrow. They may be 6 mm. antero-posteriorly 
and less than 1 mm. in greatest breadth. Fully half the length of the body is formed 
by the post-abdomen, but the separation into regions is not distinct superficially.^ 
The Ascidiozooids are of an opaque yellowish-brown colour, they are not arranged in 
systems. 
The Test is soft and flexible, it is semi-transparent, and allows the bodies of the 
Ascidiozooids to show through distinctly. The matrix is clear, but is slightly fibrillated 
in some parts. The test cells are not very numerous. They are mostly rounded or 
fusiform in shape. There are no bladder cells. 
The Mantle is moderately muscular, most of the muscle bands run longitudinally. 
The sphincter at the branchial aperture is well developed. 
The Branchial Sac is small and its walls are opaque. The stigmata are very minute 
and inconspicuous. 
The Endostyle is wide and has a very undulating course. 
The Tentacles are rather long and narrow, and are of difierent lengths. 
The Alimentary Canal is of moderate length, and the stomach is rather large. 
The Post- Abdomen is large, and contains both male and female reproductive organs. 
Locality. — Station 313, January 20, 1876 ; lat. 52° 20' S., long. 67° 39' W.; depth, 
55 fathoms ; bottom, sand ; bottom temperature, 47° ’8 F. 
Three small colonies from Station 313 have been placed in this species. They are all 
difierent, but may, I think, be conveniently regarded as slight variations of one species. 
The colony from which the above description and measurements were taken is more 
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