TUNICATA. 13 
MoLcGuLa BACCA. 
(Plate IV., figs. 1-5.) 
Locality.— Winter Quarters, in McMurdo Bay. A single specimen, measuring in 
length of body 2°2 cm., breadth 1°6 cm., length of stalk 0°4 cm. 
External Appearance.— Body pyriform, nearly globular, attached by a short 
posteriorly placed stalk (Plate IV., figs. 1, 2). Anterior end rounded, bearing both 
apertures, which are small, but distinct. The surface is absolutely smooth and shining. 
Colour pale yellowish grey. 
Test thin as tissue paper, membranous and transparent. A few foraminifera and 
minute sand grains adhere to the test round the atrial aperture. 
Mantle thin, but with delicate muscle bands and well-marked sphincters. 
Branchial Sac very delicate, with seven folds on each side. There are five or six 
bars on a fold, and three between. Many of the stigmata are long and narrow, or 
nearly straight—especially those next the endostyle and in the middle of the inter- 
spaces ; while they are coiled in well-marked infundibula in the branchial folds (fig. 3). 
Dorsal Lamina a plain narrow membrane. 
Tentacles branched, eight large and eight small, placed alternately, with a number 
of still smaller ones between (fig. 5). 
Dorsal Tubercle narrow, elongated antero-posteriorly (fig. 5), with the opening 
directed laterally and both horns turned inwards. The tubercle lies upon the nerve 
ganglion. 
Alimentary Canal showing through the test upon the left side of the body. The 
intestine is long and narrow and makes a circular loop. The rectum is closely adherent 
to the stomach (fig. 4). 
This species is closely related to the last, but differs so remarkably in external 
appearance and ina few other points that it seems impossible to regard them as the same. 
The body is here very much more globular and the stalk is much shorter. The two 
apertures are equally anterior, and the siphons are relatively smaller. The single 
specimen was tensely filled with fluid, but when pierced at once collapsed to a flabby 
“membrane. In the living state it was probably distended with sea water and nearly 
globular in form. , 
Our present species shows some superficial resemblance to the Molgula chrystallina 
of H. P. C. Mller, the Pera pellucida of Stimpson, but differs considerably in internal 
organisation, as that northern species has only five branchial folds on each side, while 
the present southern one has seven. Moreover, there are larger numbers of bars on the 
folds here—otherwise the branchial sacs are rather alike in their details. The dorsal 
tubercles in the two species are somewhat similar, and the course of the alimentary canal 
is the same in both. All this is rather curious, and suggests that we have in M. bacca 
a representative species to M. chrystallina of the northern hemisphere; but I must 
FQ 
