7 1 THE VOYAGE OF H.M.S. CHALLENGER. 



smaller placed alternately with the larger ones (PL IV. fig. 5). In minute structure, 

 the test is very compact (PL IV. fig. 8), having a close homogeneous matrix (t.m.), in 

 which large fusiform and stellate distinctly nucleated protoplasts (t.c.) are scattered. In 

 i lie protoplasm of some of these, clear spaces or vacuoles are visible, and these seem in 

 process of becoming converted into bladder-cells, but no true bladder-cells and no pig- 

 ment-corpuscles were noticed. 



The mantle is thick and dark coloured, but is not very muscular, the chief fibres 

 being a series of bands radiating from each aperture (PL IV. fig. 7, m.b.), and the 

 sphincters. There are also much finer irregular bundles of fibres all through the 

 mantle. 



The branchial sac is peculiarly thick and opaque (PL IV. fig. 6). The network 

 formed by the transverse vessels is strong, and there are broad horizontal membranes 

 hanging from most of the transverse vessels and attached by their ends to the internal 

 longitudinal bars. The stigmata are small, as the interstigmatic tubes, like all the vessels 

 in this sac, are strong. 



The dorsal tubercle is enclosed in a triangular peritubercular area, and has a reniform 

 shape with the greatest length antero-posterior. Both horns are coiled inwards and form 

 close spirals, the posterior being the larger. 



The oesophageal aperture is a little more than one-third of the way down, and the 

 oesophagus curves ventrally and posteriorly. The stomach is not clearly defined, and the 

 intestine turns anteriorly and then dorsally for a short distance, then curves abruptly on 

 itself and returns on the anterior side of the former part, and, closely pressed to it, passes 

 the oesophagus and ends near the atrial aperture. The genital gland on the left side lies 

 in front of the intestine on the ventral side of the rectum. The gland on the left side 

 (PL IV. fig. 7, g.) lies near the dorsal margin in front of the large crescentic renal sac 

 (PL IV. fig. 7, r.o.), which contains, occupying its centre, a large pulpy elongated mass full 

 of black concretions. 



Lesson's specimens were got at Port Louis, Falkland Islands. Cunningham obtained 

 his at Gregory Bay, in the Straits of Magellan, and at Stanley Harbour, Falkland Islands. 



The Challenger brought home six specimens from the Falklands, at Station 315, 

 January 27, 187G; lat. 51° 40' S., long. 57° 50' W. ; depth, 5 to 12 fathoms; bottom, 

 sand and gravel. 



Molgula peduneulata, Herdman (PL V. figs. 1-3). 



Molgula peduncvlata, Herdman, Preliminary Eeport, Proc. Eoy. Soc. Edin., 1880-81, p. 234. 



External Appearance. — The shape is between irregularly spherical and pyriform, 

 it is elongated transversely, and slightly compressed laterally ; the ventral edge forms 

 a short thick stalk while the rest of the body is globular. The anterior end is flat and 

 broad, and becomes continuous at its ventral edge with the short stalk. The dorsal edge 



