300 
THE VOYAGE OF H.M.S. CHALLENGER. 
I 
along tlie tliorax near tlie dorsal edge until it readies the oesophageal aperture, around 
which it curves so as to meet and join its fellow of the opposite side on the posterior 
surface of the oesophagus (PL XLI. fig. 5). From this point the single muscle band 
runs downwards into the test below the Ascidiozooid, where it gradually spreads outwards 
and ends. In all probability this is a retractor muscle for drawing the anterior end of 
the Ascidiozooid downwards into the colony. It would probably also compress the 
l)ranchial sac so as to expel the contained water, and would at the same time help to 
tighten the branchial sphincter, with which it is continuous anteriorly. 
Sections of this retractor muscle are met with occasionally in sections of the test 
(PI. XLI. fig. 5), and more rarely short ectodermal vessels with dilated bulbous ends are 
seen. The latter form of appendage is very short in this species. It springs from the 
region of the oesophageal aperture, and runs posteriorly or dorsally (PL XLI. figs. 5, 7,v.) 
The branchial sac is short and wide. . Its dorsal edge is straight, and its ventral 
edge is curved. The stigmata are large. They are not quite so numerous as in Lepto- 
clinum carpenteri. The ciliated cells are distinct ; and they are columnar in shape. The 
endostyle is particularly large and convoluted (PL XLI. fig. 7,en.). The dorsal languets 
are few but large. They are of elongated triangular form. 
The oesophagus arises at the dorsal edge of the posterior end of the branchial sac, 
and at first runs dorsally so as to pass through the loop formed by the two branches of 
the retractor muscle (PL XLI. figs. 5, 7, ce.). It then turns posteriorly to open into 
the large fusiform stomach. Transverse sections show the stomach as a simple circular 
cavity without any ridges or other thickenings on its wall. The intestine is narrow and 
simple. It lies alongside the stomach and oesophagus, and consequently the intestinal 
loop is narrow. 
Sections of the large rounded testis were found in some of the Ascidiozooids, but 
no ova and no embryos were discovered in any part of the colony, 
Leptoclinum edwardsi,^ n. sp. (PL XXXIX. figs. 12-15). 
The Colony is of irregular form, and is attached by the whole of the lower surface. 
The upper surface is convex and moderately smooth. The colour is grey. 
The length is about 3 cm., the breadth is 7 mm., and the thickness is about 3 mm. 
The Ascidiozooids are fairly large and numerous. They are distributed evenly ovei' 
the surface, and do not form definite systems. A few common cloacal apertures are 
])resent. The l)ody of the Ascidiozooid is placed vertically in the test, and is divided 
into two regions, thorax and abdomen. 
The Test is firm l)ut not hard. It is of a warm greyish colour, and is nearly opaque, 
'fhe matrix is densely crowded with large granular test cells and with calcareous 
* Named in honour of the late Professor H. Milne-Edwards who founded the genus Leptoclinum. 
